Q: External power, 5v or 3v, current?

[Stephanie]

I'm looking to assemble this kit tonight (found it at Adafruit.com) and have some questions about powering it externally rather than using AAA batteries.

I plan to connect the geiger counter to an Arduino mega which is running at 5vdc. Ideally I'd just tie the geiger counter's + and - lines to Vcc and Ground on the Arduino, but I wanted to confirm first if that would mess things up on the HV section of the geiger counter.

If running it at 5v is a Bad Idea, I do have a 3v linear regulator that I could drop in, but my regulator is only rated up to about 250 mA and I don't know if that is enough. Do you know what sort of current the geiger counter draws?

Thank you!

[mightyohm]

The kit runs at 3V and about 10mA (a little more with the LED on). 250mA is more than enough.

It should be possible to run everything at 5V. I would recommend increasing R6 to around 2.2K to avoid overstressing the HV switching transistor Q1, and increasing R11 to 330 Ohms to avoid blowing the LED.

[Stephanie]

Wow thank you for such a fast reply!

10 mA is great news, I imagine this must run for quite a long time on a pair of AAA batteries.

I think I'll put the kit together as intended and then just employ the voltage regulator when it's running from the external 5v supply.

Cheers!

[wbp]

The Mega has a 3.3 V supply which is rated at 50 ma. If you don't have anything else using it, that's more than enough to run the geiger counter. Why not just use that?

William