Peering inside the Melnor control unit

A project log for Hacking the Melnor 53280 into an iOT Timer

Creating a replacement for the Melnor timer, one that allows for easy timing of multiple valve units in a web interface.

laurentopialaurentopia 07/26/2018 at 18:130 Comments

Disassembly of the Control Unit was easy, methodically unscrew each screw inside the white silicone, cut the white silicon at the edges and pry open the lid with a constant force.

Control cable on the far right, red, white,green,blue, brown, unused,unused, you can see the ground line on the PCB, 3rd pin from the top. The quartz is that tin can at the top, I can't see the model number but whatever it is, it sucks given the amount of drift every month. The big flat chip next to it is a TI MCU, according to the datasheet, it includes an LCD driver so it has tons of IO, ADC and ... is ultra low power for 1$, the ESP32 will have a hard timing matching that. 

At the bottom there are fairly large capacitors which are probably responsible for that control double 16V pulse and loads of small SMD caps to keep the MCU alive when the battery is nearly empty. The many many transistor in the bottom left rail are probably used as switches to send the 16V pulse to the proper wire, and a couple of diodes sprinkled around which I think are there to prevent electricity from backing up and frying the MCU when the solenoid switches. 

Callin Calin explained that U2 and L1 form a buck converter which role is to control the feeding of the capacitor and signal to the MCU when it's full and ready to send the signal.

Overall it looks minimalist and, being someone who knows little about electronic and spends most of his time in software land, I find it elegant.

And here is a side view to get the capacitor models

The other side of the PCB with buttons and LCD, the LCD fell off, it was not even attached, very interesting choices in this box!

with the button contacts at the bottom and the row of LCD contacts

The LCD panel somehow gets signal via this gray rubber line on...