Even though there are plenty of similar modules on the market I felt the need to design my own relay module.
- Primarily because I did not have one handy when I needed. And these modules are two months away from me.
- Secondly because I wanted to test the project with components chosen by me (through-hole, easy to find)
- And because in the future I will design a series of integrated modules (more complex modules) that will have 1…16 relays. Some with RS232, RS485/RS422, Ethernet, USB connections and/or some with and MODBUS, PROFIBUS, CANopen capabilities.
So here come the design files, circuit diagrams, made with gEDA Suite. The schematic is simple, even banal, by the book. As always, the values are the result of a compromise between consumption, stability and requirements from the datasheet.
But PCB design is not quite so simple. First I have not found a footprint for my terminal block connector (chosen for low price and availability). After that it was necessary to take some decisions regarding use or not of a ground plane, dimensions of some traces. Since this project(a more advanced form) will come eventually be sent to a PCB factory, it was necessary much attention to the smallest details.
Now that the project is validated for one relay, it would be interesting to see how it scales to 4 relays.