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2013-02-04 23:56:49 (0 comments, 2 reshares, 1 +1s)

Trigger boards are here

After a couple of days to get from China to Oxford, and then a few more days to get from Oxford to my college in Oxford, my trigger boards are here. They look really good. 10 boards cost me about £30 and took about a week and a half for fabrication and delivery. I did realise one mistake that I had made in the design, so I need to put a jumper between the digital to analog converter's (DAC) latch pin. I soldered up a DAC to one of the boards but didn't quite finish writing the software library to try it out yet.

2013-01-28 23:11:30 (0 comments, 0 reshares, 0 +1s)

Much overdue update

I've got a final year undergrad working on the cosmic ray detector now, so hopefully the development will start speeding ahead again. I designed some trigger PCBs that should be on their way over from China by now. I got them made by www.hackvana.com, who have a special of 10, 5 cm by 5 cm boards for ~£13. When the boards arrive the plan will be to start searching for coincidences between two SiPM channels, so hopefully we can pick out cosmic events from the sensor's high dark count.

2012-12-10 14:56:19 (0 comments, 0 reshares, 2 +1s)

Sending data from a remote sensor

Over the weekend I was playing around with methods for sending data from an #mbed  to a server over 3G. I'm not sure at the moment whether this type of system would be good for a network of cosmic ray detectors.

2012-11-19 23:08:06 (0 comments, 0 reshares, 2 +1s)

TWEPP Paper Submitted

I didn't get into the lab today, but over the weekend I got my paper for the Topical Workshop on Electronics for Particle Physics submitted. The paper gives some details of the cosmic ray detector I'm building. Now that it is submitted I need to wait for comments from a couple of reviewers, then hopefully it will be published near the end of the year or early next year. TWEPP proceedings are published in the Journal of Instrumentation (http://iopscience.iop.org/1748-0221/) and I think they are freely available to the public.

I also found out last week that I will be supervising a final year undergraduate student next term. He will be working on the cosmic ray detector and hopefully making a high altitude measurement. This means I need to get the analog readout PCBs made up so that we can get two channels running when he starts to try and detect a... more »

2012-11-12 09:19:50 (1 comments, 1 reshares, 3 +1s)

Getting online using 3G

The #mbed  team released their Vodafone 3G library a couple of weeks ago (see http://mbed.org/blog/entry/Vodafone-USB-Modem-driver-released/ ) . I'd bought a dongle some time back when it was in beta testing, but only just  got around to testing it out.

Setting up the circuit for the mbed should be pretty easy since it simply needs a regulated power supply, a USB socket and some pull down resistors for the USB data lines. Unfortunately my dim eyes picked out the wrong resistor at first, so I spent a decent time scratching my head about why it wasn't connecting. With that problem fixed it was simply a case of trying a couple of the different networks until I found the correct one for my data plan (turns out it's £5 for 30 days, up to 250MB).

I plan to have the 3G be a backup connection method for either my cosmic ray detector orth... more »

2012-10-29 14:37:11 (1 comments, 0 reshares, 5 +1s)

Back to work

You may have noticed I haven't posted anything for a while. That was because I was away getting married and then honeymooning over in Hawaii (which is an awesome place, I suggest you visit if you can). However I'm now back in Oxford and starting to work again. The first thing to do is to write up my contribution for the proceedings of the Topical Workshop on Electronics for Particle Physics, which I went to just before I left to get married. It will be a short paper giving some more details of my prototype cosmic ray detector. I have to submit the paper in the next few days and the proceedings should be published in JINST in a few months.

2012-09-12 21:03:25 (0 comments, 0 reshares, 4 +1s)

Today I put together a poster about my cosmic ray detector for the Topical Workshop on Electronics for Particle Physics that we're hosting in Oxford next week. Here are some photos I took for it.

2012-09-10 12:02:10 (0 comments, 0 reshares, 1 +1s)

Outreach Project

I've finally found some Monday Geekery time to work on my detector today. I'll be getting into the lab later in the afternoon, but first I am working on an application for an outreach grant.

I'm asking the STFC for some money to deploy my detectors in local schools for GCSE (15 year old) students to do some experiments in their schools. We will also get the students to launch, track and recover detectors launched on high altitude balloons to measure the cosmic ray flux at high altitude. Along with the experimetns the kids will do I'm also planning a series of online lectures related to cosmic ray physics and the experiments they will do.

I need to get the application done pretty quickly (before I go on a break to get married), but then won't hear whether we receive the grant until late this year. I think the school project would be... more »

2012-08-28 07:44:33 (0 comments, 0 reshares, 0 +1s)

Designing detector PCBs

After a couple of weeks of focussing on my ATLAS work I took advantage of the bank holiday to spend the day working on my detector design. I need to get some PCBs ordered soon in order to have a prototype ready before the TWEPP conference. It looks like I'm going to be using almost all of the #mbed 's pins, and I thought routing all the connections might be a real pain, but things seemed to arrange themselves OK.

Here are some early sketches of the various parts of the circuit. Hopefully there aren't any major errors, but if you spot anything dodgy then let me know. The full design will be available under an open source license (probably the CERN one) when I send it off for fabrication.

Permalink: bit.ly/mbedCosmic5

2012-08-08 12:24:20 (0 comments, 0 reshares, 0 +1s)

Using the new scintillator and sending data to the web

As I mentioned I've got some new scintillator and wavelength shifting fibre to use. The hard part about using the fibre is setting it up so that the 1mm diameter fibre is pointing at the 1mm diameter photomultiplier. I've had a couple of small aluminium pieces made up with a recess for the sensors to sit in and a hole through to the other side for the fibre that I hope lines up with the active part of the sensor. I'm running some tests at the moment to work out if this the alignment is right by seeing if I can actually see any extra events comparing the sensor in the dark to it connected to the fibre.

I also got my #mbed  sending the data to a web socket, so I can leave it running on its own, without a computer to store the data. I then have one of my servers connect to the web socket too and dump the data into... more »

2012-08-06 16:21:46 (0 comments, 0 reshares, 2 +1s)

New scintillator and trigger board

Since I didn't seem to be sensitive to much of my scintillator I'm trying out a new piece of scintillator. This has a length of wavelength shifting fibre through its centre. With this set up I should be sensitive to cosmic rays going through the whole length of the scintillator block. The scintillation light only has to make it from where the cosmic ray went through to the fibre in the centre. A small amount of the light should get coupled to the wavelength shifting fibre. The fibre should be pointing at my silicon photomultiplier, so any light getting into the fibre should fall onto the photomultiplier.

I also found out that I cannot use my old trigger board with the new SiPMs running at the suggested voltage. The signals I get out are too large compared to the trigger threshold I can set. I've soldered up my second board with a... more »

2012-07-30 13:58:15 (0 comments, 0 reshares, 1 +1s)

Searching for signal from my new sensors

After playing around with my circuitry to power my sensor and do some amplification of the signal I'm searching around trying to find some signal. It doesn't help that my power supply is crappy and old, although there's a better one I should be able to use now that I don't need such a high voltage. I've managed to find something that looks like a signal. It's not quite as sharp as the previous SiPMs, and it's not very large, but that might be because I'm on the edge of the parameters I need.

Permalink: bit.ly/MG30Jul2012a 

2012-07-30 12:57:43 (1 comments, 0 reshares, 1 +1s)

New sensors!

My new silicon photmultipliers arrived from sensl last week. These are the same technology as the sensor I'm currently using in my cosmic ray detector, but they run at a lower voltage. These SiPMs have a breakdown voltage of around 27 V, so I'll be running them at around 29 V. This is useful since the lower voltage is safer, and doesn't need to be completely enclosed in a box. This won't make a huge difference to my benchtop testing, but hopefully one day I'll be giving these detectors to some school kids and undergrad students to use, and then the lower voltage will make the safety issue much easier.

Today I'll be trying these guys out and doing some comparisons with the 72 V SiPM I've currently been using.

Permalink: bit.ly/MG30Jul2012

2012-07-16 13:57:12 (0 comments, 0 reshares, 2 +1s)

Raspberry Pi sending images from the edge of space

At the weekend Dave Akerman launched a high altitude balloon with a raspberry pi payload. The RPi took photos with a webcam and transmitted them live during the flight from the edge of space. I tagged along to help with the launch and recovery of the payload, it was pretty fun. Great seeing the photos arriving in real time via a handful of people listening in with amateur radios across the UK.

2012-07-09 22:21:45 (0 comments, 3 reshares, 4 +1s)

Data logger

Today I made some more progress with my data logger. Basically I want this thing to be easy to use. You can just edit a simple configuration text file on your SD card and the mbed will read that and set itself up to read inputs and scan through output values. These will get saved to the SD card and also, optionally, sent over the ethernet connection to be saved on a MySQL database on a remote server.

I've now got the output scanning working (for the analog output, pulse width modulation outputs and digital outputs. The analog and digital inputs can be polled, or triggers can be counted. This means I can now use the device for logging my cosmic ray detector (which needs to scan through the analog voltage threshold and count triggers).

I've not reimplemented the MySQL stuff, or setting the clock via the internet, but I had done that previously, so it... more »

2012-07-02 20:40:14 (2 comments, 1 reshares, 3 +1s)

Ultrasound Range Finder

A couple of weeks ago I got a free ultrasound range finder from Seeed via #mbed . Today I got it working. It was pretty easy. The range finder has three connections. Vcc, GND and signal. Vcc is designed for 5V but it seems to work fine with 3.3V too. To trigger a measurement a short high pulse needs to be sent on the signal line. The range finder then does its thing and sends a pulse back on the signal line. The length of the pulse corresponds to the distance measured.

I got this working with some very simple code that simply sends the trigger pulse, waits for the start of the result pulse to start a timer and then stops the timer at the end of the pulse. This seems to work fairly well. As a bit more of a challenge I might try to get it working using the LPC1768's timer registers at some point. I'll publish my code over at mbed.org soon.
... more »

2012-06-21 17:10:32 (0 comments, 0 reshares, 0 +1s)

There's starting to be a push to get a hackspace set up in Oxford. This would be a place for people to get together and mix with others who like making things, get access to tools and expertise they don't personally have and hopefully make some awesome things. 

Please circle the page if you think hackspaces are cool. If you're local make sure to say hello too as we're trying to get more people involved.

2012-06-19 08:59:59 (0 comments, 0 reshares, 1 +1s)

Data logger update

I spent a lot of time yesterday writing up the code for my data logger. Enough that when I looked up it was almost midnight so I went home rather than post.

The current logger only uses the SD card. Later I'll reimplement logging data to a MySQL server over the ethernet connection. After starting the logger reads a text file on the SD card for configuration. This tells it the file name for storing logged data, the time period between measurements and a list of analog and digital input pins to use for measurements each period. Currently the measurements are saved onto the SD card and also transmitted over serial (via USB to a computer).

Implementing the MySQL and adding a trigger counting input should be fairly straight forward, but first I really need to make sure that the logger is robust. For example it should keep running happily even if you... more »

2012-06-15 22:20:40 (0 comments, 1 reshares, 1 +1s)

The guys at mbed.org gave me a free ultrasound range finder :D

2012-06-13 23:14:18 (0 comments, 0 reshares, 0 +1s)

Playing with some new breakout boards for my mbed

A had a few breakout boards arrive yesterday so I spent the evening playing around with my #mbed . It was pretty easy to get them hooked up and some simple code written to log data to an SD card and also over ethernet to a mysql database on my laptop. I'm planning to write a simple configuration to set up logging various data, saving them to SD and plotting them in realtime on a web page via MySQL.

2012-06-11 23:15:34 (0 comments, 0 reshares, 3 +1s)

Some detector measurements

I've been trying to make some measurements to show that my cosmic ray detector is working. Showing it's able to detect when I'm using a radiation source is fairly easy. I've run a number of times scanning through the trigger threshold voltage and moving the source around to try and gauge how much of the block of scintillator I am actually sensitive to. The right plot shows the results with the source at a few distances (in units of squares from a piece of paper - I really should actually measure it soon). This shows the signal is still detectable when the source is about 8 cm away from the photomultiplier. Probably a signal from further away (with less photons hitting the photomultiplier) is also detected, but it's swamped by a high noise rate as the threshold is lowered.

I've tried to show that the detector can actually detect... more »

2012-06-05 16:47:23 (0 comments, 1 reshares, 1 +1s)

Raspberry Pi data logger

I don't yet have an sd card hooked up to my #mbed  to store data during the long runs I've been doing to check out it's performance. Currently the mbed sends me the data over a usb cable. I don't want to leave my laptop here all the time. 

Luckily I've had a +Raspberry Pi for a couple of weeks now. So I've hooked it up in my lab to log the data from my detector. It should also be sending my data to a server I can access remotely, but since the Queen told us not to work for a couple of days the Pi isn't registered on our network yet. Hopefully soon it will enable remote data viewing.

One day this functionality will be ported over the mbed (once I've got it hooked up with an SD card and Ethernet port), but for now my Pi is doing the job well.

Permalink: bit.ly/mbedCosmic2

2012-06-05 14:50:42 (0 comments, 0 reshares, 2 +1s)

Preamplifier for cosmic ray detector

I got my cosmic ray detector working and counting events but it was counting a lot of noise when I used a low trigger threshold. I think that a lot of the problem was the circuitry around the silicon photomultiplier. I'd made up a board for the comparator and monostable that kept everything close together, had capacitance to ground where I needed it, etc, but the circuit around the SiPM was a massive, ugly, piece of strip board that I knocked together about as soon as I got my hands on a SiPM. 

+Antonin Vacheret, who is the kind guy who lent me the SiPM in the first place, also gave me an op-amp board to try out. I replaced my ugly strip board circuit with this and it helped a lot. This board adds a little headache, in that it needs -5 V, GND and +5 V inputs. When I eventually move to a portable solution that can run on battery power... more »

2012-06-05 13:44:11 (0 comments, 0 reshares, 0 +1s)

mbed cosmic ray detector

I'd always planned to base my cosmic ray detector system on an #mbed   microcontroller. These microcontrollers run on +ARM Cortex M series chips. I have the more powerful Cortex M3 version, which is a 32 bit chip running at 96MHz. The mbed is designed to be easy to get started with, similar to an #arduino ,  but running a more powerful chip. There's a browser based development environment that allows you to write and share code and compiles a binary that you simply move onto the mbed's memory as you would move a normal file to a usb stick. These are cool microcontrollers and  I'd suggest anyone interested in physical computing check them out at mbed.org.

Unfortunately when I had my detector ready to talk to a microcontroller I found that my mbed wasn't working and had to temporarily use an arduino instead. This  made my initialtest... more »

2012-06-05 13:15:37 (0 comments, 0 reshares, 1 +1s)

Cosmic Ray detector updates

I made some good progress over the last week on my prototype cosmic ray detector. I got it to a stage where it's triggering on what look like scintillation events. I hooked up a microcontroller to count the event rate. I implemented an amplifier that I was given and started taking some preliminary data that I hope will prove that the device can actually detect cosmic rays and to help me make a next iteration.

I also had some good news about a possible launch on a high altitude balloon. I've been chatting to members of the UK High Altitude Society http://ukhas.org.uk . There's a good community of balloonists in the UK (and elsewhere around Europe, Australia and the US)  who hang out at Freenode's #highaltitude  IRC channel. A few members are interested in my hope to launch my cosmic ray detector and I even had an offer from someonet... more »

2012-05-28 18:19:32 (0 comments, 1 reshares, 5 +1s)

Arduino cosmic ray detector

My mbed is acting up (or perhaps acting dead?), so I hooked up the cosmic ray detector to my #arduino . I just have it simply counting the event rate at the moment. Soon I need to do a bunch of measurements measuring the event rates with different comparison voltages and with/without the scintillator and/or the radiation source to show that what I'm doing really is detecting cosmic rays. I'll leave that for another day though because I want to go celebrate.

I'll also try to diagnose the problem with my mbed because it'd be really handy to have its analog output to set the comparison threshold.

Permalink: bit.ly/KyNeQH

2012-05-28 16:07:58 (0 comments, 0 reshares, 1 +1s)

It works!

A quick position swap for capacitor and the resistor and a much lower capacitance and suddenly it works. The red trace shows the small and fast signal from my silicon photomultiplier. The yellow trace shows the output of my board switching from 0 V to 5 V with a much longer pulse length (~4 micro seconds).

Now I need to see whether my mbed is happy with this output signal.

Permalink: bit.ly/KA2DAE

2012-05-28 15:33:17 (0 comments, 0 reshares, 0 +1s)

Circuit board half working

After playing around for a while I managed to convince myself that the comparator half of my circuit board works. I had some problems for a while because of the high impedance connection to my oscilloscope that confused me. After switching it for a probe it looks like it's working. If I probed after the first inverter then I see a signal of 5 V drop to 0 V when I get an above threshold cosmic signal.

Now I'm trying to get the monostable part working. This part of the circuit is meant to take the fast (~10 ns) pulse and stretch it to ~10 microseconds. Unfortunately it seems that the design that I had for this part of the circuit is wrong. The way I've got it at the moment I have a voltage part way through my circuit that gets pulled negative, so the output is always 0.

I'm trying to work out if there's some way I can hack... more »

2012-05-22 18:58:17 (4 comments, 0 reshares, 1 +1s)

A big signal from the comparator

I've added another couple of photos because I saw something crazy.

I increased the comparator chip voltage to 5V and had a reasonable comparison voltage (my circuit reduces the 3.3V to around 30mV). With this signal from the silicon photomultiplier (which isn't abnormally large) the comparator gave a big >5V turn on and then some oscillations. This seemed to dump some small oscillations into the signal line too.

Interestingly, before the signal the comparator output was only ~0.2V, but afterwards it settled to ~2.5V and so the circuit stopped working. I'll show this to some better electricians tomorrow and see if helps explain why my output gets stuck above 0V.

Permalink: http://bit.ly/LkgqMq

2012-05-22 18:31:46 (0 comments, 0 reshares, 1 +1s)

Starting to see some signal...

Lots of twisting wires and moving them away from each other and I start to get rid of my noise problems. For some reason that I don't understand my comparator outputs a small (~1V) signal unless the comparison voltage is much higher than the signal voltage. This is not ideal and I need to work out why it's happening, but at least now a "low" signal from my comparator isn't just a load of noise.

I'm starting to see the comparator turn on when there's a signal from the silicon photomultiplier. It's not yet the jump up to 3V that I need, but at least an output pulse of around 1/4 V is a step in the right direction.

Permalink: http://bit.ly/Ld3VPH

2012-05-22 17:57:44 (1 comments, 0 reshares, 1 +1s)

More circuit debugging

I've decided to to try and get my comparator working well with a DC input because it was not really working with my detector's quick output pulse. I worked out there's a lot of noise around the place so I'm trying to get rid of it.

Animal sums up my how I feel pretty well.

2012-05-22 13:50:47 (0 comments, 0 reshares, 0 +1s)

Debugging my circuit board

I've found at least one problem with my circuit board. It's similar to the problems that I had with the screw terminals yesterday. Basically I'm using a simple two layer board which has a layer of copper on either side of the board. To connect components a hole is drilled through the board and there's a copper pad on either side. Since it's a simple 2 layer board there is no electrical connection between the pads on either side. For the connections where I have a wire coming in on the top layer I need to solder the component on the bottom side but have an electrical connection through to the top side. My fix for the screw terminals was to solder a thin wire through as well as the terminal so that the bottom solder connects to the upper layer's trace too.

Unfortunately I can't get this working with the blue variable resistor... more »

2012-05-21 19:27:14 (0 comments, 0 reshares, 0 +1s)

Testing out my cosmic ray detector's circuit board

Last week I got my circuit board made and semi populated it with components to do some initial tests. Today I managed to get into the lab briefly to test it.

First I found out that I had messed something up when I was soldering on the screw terminals, so I spent a little time fixing that. Then I got my detector up and running and tried to simply hook up my new circuit board. Unfortunately it didn't just plug in and play well, so I'll have to do some debugging tomorrow.

I've been probing around the circuit and something weird is going on with my comparison voltage. Hopefully by fix for the screw terminal's incorrect soldering didn't screw this up, but I've got a spare board and some spare chips just in case.

2012-05-16 16:45:10 (1 comments, 0 reshares, 1 +1s)

Cosmic ray detector's circuit board partially populated

The circuit board that I designed for my cosmic ray detector has two parts. The first is where the signal from the silicon photomultiplier is compared to a tunable reference voltage to give a 5V signal when each time a cosmic ray signal is seen. The second part is to feed this signal into a monostable to stretch it out in time and also make any bumping around less of an issue. I've populated the components for the first part.

This was my first time soldering a number of surface mount devices. They are pretty fiddly but generally it went well. Unfortunately I forgot about one of the resistors until after I had pretty much surrounded it with screw terminals and the potentiometer, so getting that last one done was a but of a pain.

I'll test the first part of the circuit and if it works as expected... more »

2012-05-14 20:48:26 (1 comments, 0 reshares, 1 +1s)

Home made photogate

Since using a pre-made photogate in an arduino speedometer exercise is really easy I thought maybe the more electronically inclined students could make their own. I've knocked together a quick circuit to do it using an LED, light dependent resistor and a comparator chip. I've used a potentiometer so I could tune a voltage to compare against the voltage from the potential divider the light dependent resistor is in. I'd like to change it to an infra red system but I didn't have the suitable parts to hand and the workshop closed a few hours ago.

This output of this circuit should work with the #arduino sketch I used in my previous post (bit.ly/LKhHeK). Sorry the photos and video aren't great, because I was using a visible LED rather than infra red I needed to turn the room lights off for it to work well. On the scope the yellow trace shows... more »

2012-05-14 19:12:54 (5 comments, 0 reshares, 1 +1s)

Arduino speedometer exercise

I've made a return to my effort to develop an undergrad lab exercise to create a speedometer using an #arduino . Previously I had a rotary encoder that I thought of using, but it sent too many pulses per rotation to measure any decent speeds (without making the discs much larger).

The lab technician found an infra red photogate so we can try and do something similar but to our specification. Hooking this up to an arduino was trivial. The arduino proved the 5V to power the photogate, which has an output that switches between 0V and 5V depending on whether the path between the IR LED and the IR photodetector is blocked. This means that using the arduino to count the pulses is really easy, this output is just hooked up to one of the arduino's interrupt pins (2 or 3 on the uno).

This seems pretty trivial to me, so I think we'll... more »

2012-05-14 16:01:04 (1 comments, 0 reshares, 0 +1s)

PCB for my cosmic detector

Speaking to some of our electronics gurus it seems that noise is a major issue for reading out my cosmic detector and getting my comparator to trigger on signals from the silicon photomultiplier. It was suggested that I try to build a single board for the circuit to get everything as close together as possible and to have a big ground plane to try and reduce the noise.

Luckily our electronics workshop is awesome so they helped me design a little board and made it for me. I'm waiting on delivery of a couple of chips but hopefully tomorrow I can go to the workshop and they'll help me populate it. I've not done any soldering of surface mount devices before, but the workshop has a good magnifier, so hopefully it won't be too hard.

Here are a couple of pictures of the finished board. They are just simple 2 layer boards. The... more »

2012-05-11 10:52:01 (0 comments, 0 reshares, 0 +1s)

I've submitted my abstract for the Topical Workshop on Electronics for Particle Physics. Hopefully I'll be presenting a poster about my cosmic ray detector whose data acquisition is based around an #mbed microcontroller. I follow my attempts to design and build the detector on my +Monday Geekery page.

The workshop will be held in Oxford this year, so I should be able to attend cheaply as I won't need any travel money. With a bit of luck I might be able to be a student helper to cut the registration cost too.

2012-05-07 17:33:44 (0 comments, 0 reshares, 1 +1s)

Post notifications

I've heard a few people talk about having a circle for followers who would like a notification of their posts. If someone notifies you of a post then you get a little message saying the post was shared directly with you, so you're less likely to miss posts if you have a busy stream.

I'm happy to set up a circle for anyone who would like such a notification. If anyone would then +1 this post or post your own reply and I'll add you to a notification circle.

2012-05-07 17:31:07 (2 comments, 0 reshares, 0 +1s)

More electronics woes

I've been messing around for a few hours in the lab with my cosmic ray detector. I have a good (although small and fast) signal from my detector that I want to make a 5V trigger on when it goes higher than some comparison voltage. I need ~5V to have a large signal for a microcontroller to use.

The problem is, when I hook up the two signals to a comparator I either drag the voltages away from what they should be or introduce a bunch of noise to the circuit that screws everything up.

I was hoping that I could get one of our electronics gurus to take a look at my circuit today, but it's a bank holiday so pretty much noone was in the department. Hopefully I'll get a chance to ask for some help tomorrow. If you yourself happen to be an electronics expert and could help then please make a comment about it.

2012-05-04 20:17:52 (0 comments, 0 reshares, 0 +1s)

Some more tinkering

After I finished my work this afternoon I got in the lab for a couple of hours. I played around for a while. I tried hard to minimise the noise in my circuit. For a while I had a fairly ugly signal coming out of the comparator that I think was actually triggered by my detector because it wouldn't happen if I took away my radiation source. Unfortunately I tried to make the signal less ugly by changing some components and couldn't get back to the ugly signal I had. I really should just take a photo or something when I make some progress. I'll see if one of our electronics experts can give me some advice on Monday.

2012-05-03 17:21:06 (1 comments, 0 reshares, 2 +1s)

Playing with my cosmic detector

I finally got some time in the lab. I'm trying to get my max999 comparator to trigger on cosmic ray events. As a first step I've got my silicon photomultiplier signal from my cosmic ray detector and also a comparison voltage from my #mbed fed into my oscilloscope.

The red line is the pulse from the detector from an event, the yellow line is the comparison voltage. Hopefully, when I get this thing working, the comparator will change it's state when the red line goes to a higher voltage than the yellow one.

2012-04-30 23:05:45 (0 comments, 0 reshares, 0 +1s)

I didn't get into the lab today. I've not quite recovered from my glandular fever (mononucleosis), so I'm not working full time yet and so I have to put off my fun to get my actual work done. Hopefully I'll get a chance later in the week. I'd really like to get my #mbed counting cosmic ray events soon.

2012-04-23 18:45:43 (0 comments, 0 reshares, 0 +1s)

MAX999 Schmitt Trigger

I've got the new fast comparator (which is a MAX999) working as a Schmitt trigger. Unlike the previous comparators this comparator can trigger on even the fastest pulse my #mbed can kick out, which is around 50 ns long. Now I just need to try it out using the actual signal from my cosmic ray detector.

In the photos the red line is the varying signal and the yellow is the output of the trigger. The trigger output goes low when the signal is larger than some threshold. First I fed it a sine wave that is relatively slow, then a pulse from my mbed turning an output on and off as fast as it can. Unlike my previous test with a standard comparator this one is able to trigger on the fastest pulse.

Permalink: http://bit.ly/I0Vu93

2012-04-23 17:09:27 (0 comments, 0 reshares, 0 +1s)

Back in the lab - got my breakout board

I'm back in the lab after 2 weeks that were meant to be a holiday but turned into fighting off a virus. I'm not yet back to 100% so I won't get as much time to play in the lab as I would like.

I got the breakout boards for my tiny surface mounted fast comparators. The boards just track out the 5 pins from the comparator to pins that I can plug into a breadboard to make my life easier. Hopefully these comparators will work fast enough to register the signal from my cosmic ray detector so that my #mbed can count the number of events.

Our technicians actually made a few of the boards, so I have some spares. I actually have a spare chip too, so hopefully if I break the one I'm using I can easily get a new one soldered to a spare board and be back up and running again quickly.

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2012-04-02 19:03:33 (0 comments, 1 reshares, 2 +1s)

Arduino Speedometer Exercise

I managed to get the rotary motion sensor working with an arduino, but it seems that it won't be useful for the experiment I am developing. The sensor has two outputs. The sensor outputs pulses when the axle is rotating, with the two outputs corresponding to the two directions of rotation. Unfortunately the pulses are 0.0001 ms long and a pulse is sent about ever 1/1400th of a rotation. This means that when the rotation speed gets to around 5 revolutions per second the pulses start to overlap and a constant output voltage is seen. The arduino therefore cannot trigger on the changing output voltage above this speed.

I did some calculations and this would require a much larger disc to be used if the speed of a mass falling under gravity. With the disc sizes available on the sensor the free fall speed would get too fast for a measurement very... more »

2012-04-02 19:06:09 (0 comments, 0 reshares, 0 +1s)

My fast comparators arrived and they are tiny

The data acquisition system for my cosmic ray detector has to be able to record a signal pulse that is only a few nanoseconds long. For this I need a fast comparator, which is able to tell when the signal goes above a set threshold before it's gone away. I ordered a couple of these and they arrived late last week. I could only find surface mount devices that I thought would work, so these things are tiny. You can just about see one in the picture. The chip is inside a weirdly shaped container (I don't want to take it out and lose/break it). You can just see the 5 pins (2 on the left, 3 on the right) and there's a biro for size comparison. These things are too small for me to deal with so I'm having a little break out board made up. The chip will be soldered to the board which will connect each of the tiny pins to a larger pin... more »

2012-03-29 21:56:35 (3 comments, 0 reshares, 1 +1s)

New Logo

I decided I should actually make a logo for +Monday Geekery rather than just using my crappy self portrait. Thanks to +Michael Chino Yap for some help designing it.

2012-03-28 14:57:32 (0 comments, 0 reshares, 0 +1s)

Undergrad Lab Arduino Speedometer Exercise

I'm designing an experiment for our undergraduates to use an +Arduino as a data acquisition system. One of the exercises I'm thinking about is having the students make a speedometer. A simple speedometer could be made using a disk with one or more slits. With an LED on one side and a LDR on the other you can trigger on the change in LDR resistance as the light hits it each time the slit passes the LED.

I'd asked our mechanical technician if he could make up a system like this he's managed to find the rotary motion sensor in the pictures. Hopefully this is pretty much what I wanted. The one drawback, though, is that this is designed to plug into a black box which is then able to interface with an ancient windows PC. I'll have to have a play around with the sensor and see how I can interface it with an arduino.... more »

2012-03-26 18:18:19 (0 comments, 0 reshares, 0 +1s)

Trigger Speed Test

I've just done a quick test to show that the comparator that I'm currently using isn't fast enough to handle the signal from my cosmic ray detector.

In the photos the yellow line is my input signal and the red line is the output of the Schmitt trigger. The time divisions are each 50 ns, the voltage divisions are 2 V. I used my mbed to give an fast input pulses of a few different lengths.

The fastest pulse is about 60 ns and it was too fast for the trigger to fully reach 0V. However a pulse of 175 ns triggered properly.

This shows that I'll have to wait until my faster comparator arrives in order to get my mbed recording data from my cosmic ray detector, which gives out pulses that are shorder than 50 ns.

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