CR2032 and no motor driver?

[Leseratte10]

I'd like to replicate this build / project but I have a few questions (so this is not really an "issue"):

First, I have found this web page http://www.idogendel.com/en/archives/507 which states that the motor driver is not really needed, because you don't necessarily have to switch the polarity of the magnetic field, turning it on and off with a transistor would be enough. Is that actually true?

Second, what about powering the circuit with a CR2032 cell? (I am aware of #17 ) The current project doesn't seem to have any discharge protection to protect the Lipo cell from over-discharge, does it?

A typical CR2032 has >200mAh, and the ATtiny needs almost nothing (0.3 µA = 0.0003 mA is what I've read, so, a battery standby time of basically infinity.

Can I just replace the Lipo battery cell with a CR2032 or does that not provide enough power for the coil? Does anyone happent to have schematics for that mod? Should / Do I need to increase the capacity of C1?

[samyk]

1. It's true, just like bypass caps aren't always needed. It might work in some cases, and in others, it won't work. Drive it properly and you will increase the readers it will work on (it's worked on all readers that I've tested). Additionally, you'll be limited by the source current of the pins, drastically limiting your output and reducing your range significantly. Thus, use a driver if you want some real current output.

2. Sure, CR2032 should be fine. The cap is necessary to charge up to provide sufficient power when activating (and it may not recharge as quickly with a CR2032, but shouldn't be a big deal). Don't forget the power used by the electromagnet in your calculations. Same size should be fine, let us know how it goes!