Simple, Compact Wireless Measurement

The layout is complete! The code uses the EFM8 Laser Bee - I chose the QFN version because it is easier to solder and this board doesn't need to be ultra compact. Going to send it off to be manufactured!

Currently I can't get my hands on a Laser Bee, so instead I'm using a Universal Bee as a temporary prototype before I shift over to the laser bee, given that the SDK and registers are mainly the same. I don't intend for this device to be updated much in the field when it has a Laser Bee on it.

Of course, if it is the Arduino version, that's a whole other story.

So it turns out that you can even find the JDY-08 breakout from Aliexpress, which means that every part of this project is now easily breadboard-able! This means that even if you don't know how to solder, you can also build a measurement circuit yourself.

Since this is meant for low voltage experimentation, it can only measure up to 3.3V. Using Arduino's native ADC which gives us 1024 counts (8-bits), if we increase the voltage range we can measure, the precision falls.

Maybe one way is to create a switch so that you can turn on high voltage measurement whenever you want to, although I think that might already be a feature creep.

The ATMEGA328P is not the best IC to do ADC measurements with, plus it is very out of stock.

I'm thinking for the final design using a Laser Bee from Silicon Labs might do the trick. It is designed specially for measuring analog signals and it is quite a low cost part. It also has USART to pass messages to the BLE module, and it wouldn't need the finagling that the ATMEGA needs to run at 3.3V.

1. My breakout board for the JDY-08 draws about 9.5mA of power @ 3.3V, and this is approximately true even when it is transmitting.

2. I have a pretty bright LED on the board so that can account for roughly 50% of the power draw.

If I use the worst-case estimate: assuming a smallish 600mAh battery (1.2V) with a 60% efficiency, with another 5mA of power draw from the ATMEGA, that is 15mA from the circuit at 3.3V = 50mW vs 432mWh, this means that a fully charged battery can last about 8 hours of continuous power draw and measurement.

Using an Alkaline battery with 2000mAh would give us approximately a day of measurement. I think this is a pretty good even without any power optimization.

It is incredible how far this chip shortage has spread. I can't find ATMEGA328P TQFP packages at any of the people I like to buy from.

I guess now I'll have to use the DIP version, although that's not too bad, since that means that the whole circuit can be prototyped on a breadoard.