Is the resistor going into the wiper of the 100K Trim-pot supposed to have a value?

Thanks.

Arv,

I think the tally counter uses a similar or perhaps identical chip to most pedometers. All the cheap ones from china look to be quite similar. There is typically two and sometimes three capacitors, an encapsulated die mounted right on the board, the LCD, some kind of switch, and an LR55 battery.

The debounce time may be set by one of those caps, but fiddling with them doesn't seem to make much difference. Removing one of them completely stops the unit from working and is probably the oscillator. Worthy of more study anyway.

Regards,

Alan

Ted,

Yes, you could use the typical "charge sensitive amplifier" topology to null much of the capacitance of the diode, but I think it will still have poorer signal to noise ratio.

Worth a try though, it would improve the bandwidth of the device if nothing else, increasing the maximum count rate. The circuit is a bit of a hack, it could be much better.

Regards,

Alan

Dear Sir,

I noted your reply to the person who asked if you had tried low cost solar cells as a large area detector.

You remarked that the extra capacitance reduces the amplitude. That made good sense to me. I went and looked at your circuit again. If I correctly understand it, you are using the diode current to develope a voltage pulse across the 10meg, and then amplifing that with the FET. Would it be possible to route the current into the virtual ground connection of an op-amp instead of the 10meg ? As a current output would that help alliviate the problem of the extra C ?

Regards

Ted Carron

While looking at your latest Ray Detector effort I noticed your "Talley Counter" and it occurred to me that the cheap "Dollar Store" type pedometer might be modifiable to make an inexpensive Talley Counter. Some time ago I tried converting one to a frequency counter only to find that they don't count reliable above a few hundred KHz, but as a Talley Counter they might be adequate. If it works then you have another source of "Cheap Instrumentation" for your workshop.

Zilvinas,

Yes, I tried using small solar cells and larger die transistors. The larger capacitance of the big devices reduces the amplitude of the pulses observed and increases the relative noise level, making the device much less sensitive to lower energy radiation.

The calculator solar cells are too noisy to make a good detector unfortunately. You can parallel several BPW34s to make a bigger detector, I have not investigated the trade-off point where you need a seperate buffer for N photodiodes to make it worthwhile... A useful experiment I must undertake.

Regards,

Alan

Hi Alan,

Nice work!

Have you considered/tried to use solar cell from cheap calculators instead of pin diode?

73 LY2SS

Peter,

Ginger beer, Bundaberg specifically.

All these sources are quite weak. You'd need to physically eat them or strap them to your body for an extended period of time to do any damage. The most dangerous is the nitrate salts of thorium and uranium, mainly from their chemical toxicity if you were to swallow them.

Regards,

Alan

Alan,

Not sick of your radiation detectors at all.

What beer are you drinking there?

These radiation sources you have... are they likely to cause you any harm?

Peter