In this Instructable I will show you how to build a 1-70 VDC, SPST NO, 0.05A 1-70 VDC relay for under $4.
Step 1: Gather Materials
Here is a list of things you need for the Instructable.
1-IR led 1.99
1-IR photo transistor 1.59
(they must be IR or the resistance will never stay the same).
Step 2: Building the Relay
First tape the IR led IR photo transistor together. Then bend all four leads down.
Step 3: Using the Relay
First connect the correct resistor (1-10v=8.2ohm,11-20v=150ohm, 21-25v=180ohm) from negative in to the negative on your supply. Then connect the positive in to the positive on your supply. After that connect the 2 positive in to the positive on your 2 supply and the 2 positive out to whatever you want. Thanks for taking a look at this Instructable please vote for it in the LED contest.