This is a simple 100mA constant current board.

It uses a handful of common components, I used through hole components to make assembly easier for DIYers.

The input voltage needs to be known so that the correct resistor can be chosen for the supply voltage, either a 33 Ohm (for 3.5-4.5V), 81 Ohm (for 6.0-8.4V), 120 Ohm (for 10-16V), 220 Ohm (for 18-30V),

It is also possible to change the output current by changing the pair of 51 Ohm resistors, for instance if they were changed to use a single 51 Ohm instead of 2 it will halve the current making it a 50mA source, if you reduce the resistance it will increase the current, so if you want a 200mA source change the 51Ohm resistors to be 25 Ohm, the BD139 can handle 1 Amp of current if it is heat sinked so it has plenty of headroom for increasing the current, only the resistors may need to be changed to higher wattage types.

This is Rev 1.1 of the board, you can see my video on the first revision of this board here: https://youtu.be/Q5cYt8L1Za8

The FULL BOM is:

51 Ohm 1W resistors x2

680 Ohm 1/4W resistor x1

33 Ohm OR 81 Ohm OR 120 Ohm OR 220 Ohm x1

TL431 x1

BD139 x1

100uF 35V Electroytic capacitor x1

100nF ceramic capacitor x2

2K Ohm 25 turn trimmer x1