This is similar to DIP AVR project 1 but with some differences.
Project one was a sensor module which needs enough power to heat the air quality sensor.
Project two is a controller which needs less power but ideally has a crystal clock for better timing accuracy.
As before in project 1 - the chip was pre-programmed and TWI uploading tested before beginning the building. The minimal compontents to flash the LED include a resonator for system clock. This was later replaced with a surface mount crystal and loading caps. My arrangement of decoupling caps was a little different and one surface mount cap was used.
There was no need for the big regulator this time so a 78l05 was used and once again a poly-fuse. My standard DIN plug arrangement was used with the minor difference being a 7 pin plug was used because I was short of 8 pin ones. I also added a few drops of CA (superglue) to stablize everything. TWI comms and uploading were then possible.
The addition of a terminal block made the device ready for use. I also added a voltage divider (not used) so the micro can sense the power buss voltage. The module was tested as is and found to be prone to resetting when the pressure dump solenoid was used. This appeared to be temperature related and more testing is needed.
The solenoid driver is opto-coupled and the power supplies are quite independent so there should not be any glitches coming back to the controller. I was perhaps loading the i/o pin a bit hard but well under the maximum limit specs - I've reduced it a bit. The solenoid drive circuit is on the pressure controller page.
This is a pressure versus time plot of the pressure in my chamber while the pressure is cycled twice by the controller.