Instructables

Two hand control

Picture of Two hand control
two-hand-control.JPG
This circuit switches on a relay by pressing two buttons at the same time (with a tolerance of 0.5 seconds). Similar circuits are used for two hand control systems of dangerous machines, such as presses. Due to these control systems the operator keeps both hands away from the dangerous parts of the machine.
Based on 555 the circuit is supplied by 12 Volts DC. If the buttons are pressed at the same time the input voltage (pin 2 and 6) gets low and the relay turns on. Otherwise the first  transistor switches on, then the operation has to be repeated.
The relay switches off after few seconds, depending on the value of the second capacitor. So the operator has to release the buttons and press them again.
This is just an hobby project, it shouldn't be used for real machine control systems.


omnibot2 years ago
Congratulations, your project is pretty much unique on the interwebz. Also it's a novel and (I think) new use of the 555. Cool!