#801 HP Torch/Laser
Fixing a laser pointer and torch powered by a 3V coin cell.
Notes
I found this dinky little laser pointer/torch device in the back of a drawer. Obviously the give-away from some previous HP event. A quick test proved it wasn’t working any longer.
A look inside and I found a coupled of problems:
- battery connections broken
- laser diode had broken from its substrate and disconnected from the board
Do I really need this device? No! But let’s fix it anyway..
Circuit Design
Quickly retracing the circuit with Fritzing: see hp-torch-laser.fzz.
It’s simple:
- one push-button switching a white LED with 60Ω current-limiting resistor
- second push-button switching a red laser unit, with a 180Ω current-limiting resistor
Build Log
I checked the white LED was still OK, so the main task is to replace the laser unit.
I have some 3V/5V 650nm 5mW red laser units. These come with a built-in 30Ω current-limiting resistor, so I’m going to remove the onboard 180Ω current-limiting resistor.
They also have a full metal bezel/heatsink/shield that was not in the original laser diode. Rather than remove it, I’ll bodge-it and cut away the case to make space.
With the new laser unit installed with some hot glue to keep it in position.
Reassembled:
Adding a panel to cover the new laser assembly:
Sprayed with some My Hobby H68 (RLM74 Gray Green) to blend the repair:
Front panel label re-attached with Bu Lai En B-7000 jewelers glue:
Testing the laser:
Testing the LED (it is not very bright):
