A few notes on this kit. I had hoped that it might be operable at 3V, but a test of this showed it doesnt. The LCD backlight works, and the unit generates a series of three bleeps as if starting, but there is no display. There is HV to the G-M tube, so it looks like its maybe just on the edge. Perhaps 3xAA to provide a 4.5V supply would work.
Anyway, I found out a USB power bank that was actually charged, and connected it up. To do so I had to piggyback the Geiger Counter onto the power terminals of a little digital clock kit that the power bank was connected to. But the kit powered up successfully, displayed its start up splash message, and went to work.
I have connected it up to my spare BOI-33 G-M tube using 1/4inch fuse clips. This is equivalent to the perennial SBM-20 tube. My test source is my trusty old WW2 radium faced pocket watch. The kits red led lights at a count rate above 50 CPS (counts per second), while the blue one flashes for each detected pulse. The top button when held switches between CPS and the bargraph display, and the uSv/h (microsieverts per hour) and CPM (counts per minute) display. The bottom button mutes/unmutes the sounder.
Two video clips show both display modes in action.
So, what next? Well, decide on a case for it, decide which tube (s) to build into the case, how to switch between them, what battery supply to provide (this means testing the 4.5v 3xAA or 3xAAA option, and possibly doing the 78L05 mod), what sort of connector to use for the interface output (9-way D type? Or 3.5mm stereo jack?) and what connector to use for an external probe. I probably wont put a switch for the HV voltage, as all my tubes work on 400V except one, and this kit cant provide the 1.6kV for that one!
On the whole, its been a pleasant build, and its a nice little kit. I would say its a tad overpriced, and the lack of an on-board regulator is a poor oversight. Suggested improvements for the manufacturer - Add an on-board regulator, make the component pitch fit better (maybe it needs a couple of extra mm of board space!), include the proper battery connector, and move to a Molex type connection for the HV rather than the screw terminal, and add a brightness control preset for the LCD. Oh, and add an option to display the PWM values and measured HV voltage.
Update! - Ive had chance to test using a 4.5V supply. Rigged up with 3x AA cells in a 4x AA holder (one place shorted out with a croc clip jumper), the Geiger Counter works flawlessly. Depending on the current drawn, most of which will be for the LCD back-light (so modifying it to have a variable resistor to set the brightness is sensible) i have no doubt it will also work perfectly well on 3x AAA, which is not only a heck of a lot cheaper than a PP3, but easy enough to fit in a case.
Testing again with 3V, the issue is not with the counter itself, which by the flickering LED and rapid clicking, works fine at 3V (the ATMEGA328 microcontroller can go down to 1.8V) but with the HD44780 LCD driver ICs, which need more than 3.3V to run.
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