So I’ve came back to my ATtiny2313 – based thermostat project, that I’ve started to work on some time ago. And today I have assembled a first prototype (actually I only need a couple of these).
If you haven’t seen video I’ve made on this project, you can watch it here: Part1 Video.
It’s based around ATMEL AVR ATtiny2313 microcontroller, it will measure temperature using DS18B20 digital temperature sensor, and it has a 30A 240VAC relay to control heater.
As you can see it consists of two boards: main thermostat board and display board.
First I etched the boards.
I had some minor problems with those multiple parallel traces that goes from MCU to the resistors. The clearance between those traces were pretty small, and I’ve put too much pressure on the iron, so they become a little bit thicker and some of them were touching each other.
This problem was solved with X-ACTO knife and magnifying glass, then I made them a little bit thinner in the Eagle board layout to increase distance between those traces, so I won’t have this problem in the future. I changed thickness of the traces from 0.016in (0.4mm) to 0.012in (0.3mm) – which is perfectly fine for DIY boards.
After that I drilled and assembled these boards. And then washed them in ultrasonic bath with isopropyl alcohol (90% rubbing alcohol).
With ultrasonic bath cleaning flux residue from boards becomes effortless. You always get a perfectly clean PCB.
Here is close-up of thermostat board:
I got to say that big transformer is a bit of overkill. I could’ve put a smaller transformer instead.
Also right now for powering relay I installed 12V voltage regulator, but this relay can pick up starting from 7V, so I guess I’ll just swap 12V regulator with 9 or 10 volts one to decrease it’s current consumption.
Bottom side of this board looks like this:
High-current mains voltage traces on the right filled with solder, so they can handle more current.
Display board top:
And the bottom:
I’ve used SMD type connector here, which allowed me to make this board single-sided.
Since the hardware part is done, it’s time to do some programming…
I will make all the files and documentation for this project available a little bit later, when I’ll finish it.
And now I will give you only schematic in PDF format:
Schematic needs a little bit of polishing, so just wait until I’ll put out the final version.