Thermostat for Etching Bath Heater

Overview

The thermometer and thermostat device has been designed specifically for homemade etching bath as it measures the temperature of the etching liquid and turns ON/OFF the heater according to a temperature window.

Details

An NTC sensor connected to a PIC16F256 microcontroller is being used by this thermostat which switches ON or OFF the relay depending on the temperature value. Two 7-segment displays are used to display the temperature value that makes the design cheaper while doing the job well as PCB etcher heater controller. the temperature thresholds in the current firmware has been set to 38°C and 42°C. If different values are needed, two constants in source have to be changed and then recompiled. Alternatively, a couple of buttons or a little modification can be added which will make it more flexible.

The relay will be actuated according to temperature wherein it is actuated on temperatures below the threshold and is released for above the threshold temperature. A 2N2222 switching transistor with 1A fuse is used to drive the relay. The device is powered by its own supply that is made up of 1N4001 diodes for half wave rectification, 7805 regulator, and 3 capacitors.