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November 17, 2012
about 2 years ago
This is a very nice little unit although it should have an adjustable integrator as it would be nice to look at surface EMG individual spike amplitudes to see how many motor units one is activating. With the electrodes positioned properly, the CMRR is amazing and got an incredibly clean signal on my Propscope. Was easily able to position the electrodes to pick up activity from the extensor indicis muscle and had a very clean waveform which entirely reflected extensor activity of my index finger from subtle movements to full movements.
This unit can be used as a crude EKG placing one of the active electrodes on the lateral lower left chest and the other over the sternum (in my case I was looking for relatively hairless areas). The ground electrode can be placed on the abdomen. The result is a clear but very low pass filtered EKG signal of which only the QRS is detectable. If one is just looking at heart rate, then this device is more than adequate. If one wants to record a full EKG, then one needs a much lower valued integration capacitor.
Having played around with recording surface EMG in the past, this device is very simple and provides a more than adequate integrated EMG signal for such applications as looking at leg movements during sleep. What it wasn’t able to do was to provide an EOG. Put the two active electrodes around my left eye, one lateral and the other inferior with the ground electrode on my chin. Only signals picked up were facial muscle activity EMG’s. Likely EOG could be picked up with this unit with a tweaking of capacitor values but it would likely be simpler to just build an EOG amplifier as the EOG is a fairly high voltage signal in relation to surface EMG waveforms.
Aside from the inability to adjust the integration time comstant (and hopefully the next version of this unit will have this feature), am quite happy with the unit and ordering more of them to monitor individual leg muscle activity while walking. My ambulatory physiologic monitor uses a 3-axis accelerometer to measure the acceleration of the monitor during walking but with 4 of these units could determine exactly what sequence of muscle activation is in the large muscle groups of one leg.
about 2 years ago
I like this device. Have had a very puzzling bug in some Propeller assembly language code that I’d been trying to debug with a crappy surplus oscilloscope and custom debugging PASM. 5 minutes after opening the package, I had the logic analyzer hooked up and found the problem. In my case, this logic analyzer paid for itself in 5 minutes. It may not be the fastest device available but the price is right, very easy to download software and quite an intuitive interface.
24 Mhz is fast enough for Propeller projects as the Propeller runs at 80 MHz taking 4 cycles/instruction. Considering that all of the SPI interfaces I do are bitbanged, it will be more than adequate to debug these. It’s not very often that I run into a piece of test equipment that’s as easy to use as this logic analyzer as I have yet to even look at the manual.
about 2 years ago
Nice product and found out I had no difficulty in picking up K40 disintegrations which actually surprised me. The integration times are long, but putting a bottle of K-citrate capsules in front of the GM tube gave 20 counts/minute which is easily distinguishable from the 15 cpm background that exists in my Kamloops basement.
The one caution about using this unit as a source of random numbers is that it’s biased. There are far too many short intervals under 100 msec and the 47 msec interval appears far more often than one would expect by chance. What I did to measure the intervals was to write a quick and dirty VB6 program which timed the occurrence of every serial byte transmitted from the Geiger counter to 1 msec precision using the windoze TimeGetTime call. Perhaps increasing the size of C9 might work, or one could “debounce” the signal in software.
That aside, the unit has exceeded my expectations and I’ll likely be ordering a few more in the near future. A more detailed description of looking at K40 counts is given at:
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