Re: homebrew multi-channel analyzer
Posted: Mon Sep 15, 2014 2:10 pm
Okay Doug - here's what I've got so far in terms of MCA:
The two boards are currently mounted back-to-back using threaded rods - those are metric, M3. I can send you some M3 nuts, if you don't have them / can't get them easily in the US. I left the connecting yellow wires long enough so that you can also mount the boards side by side and still have flexibility - you can always make them shorter, anyway.
The rear cable carries the serial signal, which is also available on a screwclamp. The pinheads on the right connect to the ICSP dongle for PIC software download.
The very left connector on the front side (i.e. facing the camera) is a "pulse-out" signal, for each pulse detected and counted, a 3.3V square impulse is generated. Intended for fast and easy "cpm" measurement, just connect it to a counter.
The rear connector on the top board is signal in from the preamp. As for supply voltage: required is 3.3V for the logic part and +/- 12V for the analog circuit.
Here's the input signal waveform that I tested the circuit with (fast rising exponential followed by slow falling exponential):
Communication settings for serial interface: 115200 baud, 8 databits, 1 stopbit, no parity.
Here's how the thing is controlled (i kept the commands pretty minimalistic to save resources and avoid unnecessary complications):
Here are some results (I just manually swept through some discrete voltage levels, so no precise timing and hence different peak heights in the spectrum):
Below 1V, however, things start to get a little nonlinear. Peaks below 300mV are not detected or smeared out to the left of the spectrum.
What do you think? If you're OK with the functionality, I'll upload the final schematics / board layouts as well as the source code and get the thing on its way to you.
-Philipp
The two boards are currently mounted back-to-back using threaded rods - those are metric, M3. I can send you some M3 nuts, if you don't have them / can't get them easily in the US. I left the connecting yellow wires long enough so that you can also mount the boards side by side and still have flexibility - you can always make them shorter, anyway.
The rear cable carries the serial signal, which is also available on a screwclamp. The pinheads on the right connect to the ICSP dongle for PIC software download.
The very left connector on the front side (i.e. facing the camera) is a "pulse-out" signal, for each pulse detected and counted, a 3.3V square impulse is generated. Intended for fast and easy "cpm" measurement, just connect it to a counter.
The rear connector on the top board is signal in from the preamp. As for supply voltage: required is 3.3V for the logic part and +/- 12V for the analog circuit.
Here's the input signal waveform that I tested the circuit with (fast rising exponential followed by slow falling exponential):
Communication settings for serial interface: 115200 baud, 8 databits, 1 stopbit, no parity.
Here's how the thing is controlled (i kept the commands pretty minimalistic to save resources and avoid unnecessary complications):
- Code: Select all
OK //MCA is started up and ready to accept commands
R //reset spectrum
OK //command carried out successfully
r //reset "total counts" register
OK
n //get "total counts" register
OK
0 //register reads zero, since it was resetted just before
h //get "last pulse height" register
OK
114 //last pulse counted was binned in channel 114
S //start acquisition
OK
s //stop acquisition
OK
c115 //read channel115
OK
6783 //# of events in ch. 115
c116 //read channel 116
OK
1314
c5000
ERR //some error checking is done, too
C //read entire spectrum
0 //ch. 1
0 //ch. 2
0
.... //all other channels (4096 channels in total) follow here
0
0 //last channel
Here are some results (I just manually swept through some discrete voltage levels, so no precise timing and hence different peak heights in the spectrum):
Below 1V, however, things start to get a little nonlinear. Peaks below 300mV are not detected or smeared out to the left of the spectrum.
What do you think? If you're OK with the functionality, I'll upload the final schematics / board layouts as well as the source code and get the thing on its way to you.
-Philipp