Stamp sized ATtiny84 remote sensor

I have been amazed by the work done by @Tobias with his “Funky” sensor, so I asked him for a permission to make my own version. The Funky is a JeeNode micro clone, less the two Jeeports and probably in 1/3 of the size. Basically it is the size of a mail stamp measuring just 21 by 22 mm in size.

I branched a version that has the battery voltage measurement circuitry removed as I can do that using the bandgap reference. The freed-up pin was routed to pad 7. Also I added a optional to solder 4.7K resistor between pads 4 and 5 thus making it possible to directly solder a DS18B20 on pads 4,5 and 6, driving the power from pad 4, data pin being pad 5 and GND is pad 6.

The next change I made is to add a voltage step-up circuit, so that theFunky can be used with a single AAA batery as well. The original design had a voltage regulator instead where the other use case is covered – powering if from higher voltage. I read that using the step-up with lithium battery doesn’t work well, so the step-up is only connected to the external battery connectors and not the CR2032

Quoting @Marcus

“Yes, lithium batteries and a step up are a sad story. I tried it myself to get more power out of a CR2023 with a step up circuit. It did not work at all.
It seems that the chemistry of the lithium batteries is very slow. So the step up depletes the areas around the internal connectors and the voltage goes down. It seems like the battery is empty after a few seconds. But it recovers after some minutes again. But it does not feel god, nor does it help.”

This way the Funky can be powered either by a CR2032 or a single AA or AAA battery. I ended up using the same step-up circuit as the Jeelab’s AA Power Board as the components are small enough to fit on Funky’s limited space PCB

Board

Schematic

And this is how it should look, photo by @Tobias  http://tobiscorner.floery.net/

As a conclusion, this was interesting project. I am not sure if I will be making PCBs or leave it just at the design stage yet, I am concerned about soldering the tiny 603 size components and the almost impossible to solder step-up circuit 🙂 ..

Eagle files are here: Funky_Sensor_2