voltagedrop
- Apr 22, 2021
- 16
- Joined
- Apr 22, 2021
- Messages
- 16
Hello, first post, just joined, and hoping to exploit some knowledge as I teach myself electronics for the fun of it.
My family uses a portable ice maker in our holiday trailer. As it makes ice, it harvests into a "bin" of its own. Near the top of the bin, is an Infrared LED, and across from it a photodiode. When the ice builds to this level, the ice blocks the IR beam, and the unit shuts down. As the ice melts, or is removed from the machine, and drops below the beam, the machine restarts.
The machine began not shutting off, and would keep producing ice, overflowing the machine, or until it ran out of water.
I disassembled and found rust coming out of the Photodiode, where the leads enter the epoxy. I acquired new a new LED and Photodiode from Digikey, a "matched pair". replaced them, ensuring the polarity was the same at the old pieces (using the flat on the epoxy for reference).
Now I have the opposite problem, and the ice making immediately goes into "ice full" mode, indicating the beam is "broken".
I measured current and voltage drop at the photodiode, 5 v across diode at 1.4 microamps. If I shine a bright flashlight into the photodiode, I can get the voltage drop to decrease and currant to increase. If I hold the new LED approx 1" or less, voltage drops to near 0, and current increases to 40-50 microamps, and unit functions as normal. As soon as I move beyond the approx 1" approx, "ice full". Fully assembled, the LED and photodiode sit approx. 7" apart.
Attached is a rough sketch of "ice full circuit".
Any ideas? Seems either the LED isn't "powerful" enough, or the Photodiode isn't sensitive enough. I played around with the LED's limiting resistor until I had it up to approx. 100mA (max per spec sheet), and the Photodiode changed very little (up to around 10 microamps). This also made the 5V linear regulator a touch warm (specs out to 100 mA max), however the regulator stays at 5V throughout.
Thanks for your thoughts.
My family uses a portable ice maker in our holiday trailer. As it makes ice, it harvests into a "bin" of its own. Near the top of the bin, is an Infrared LED, and across from it a photodiode. When the ice builds to this level, the ice blocks the IR beam, and the unit shuts down. As the ice melts, or is removed from the machine, and drops below the beam, the machine restarts.
The machine began not shutting off, and would keep producing ice, overflowing the machine, or until it ran out of water.
I disassembled and found rust coming out of the Photodiode, where the leads enter the epoxy. I acquired new a new LED and Photodiode from Digikey, a "matched pair". replaced them, ensuring the polarity was the same at the old pieces (using the flat on the epoxy for reference).
Now I have the opposite problem, and the ice making immediately goes into "ice full" mode, indicating the beam is "broken".
I measured current and voltage drop at the photodiode, 5 v across diode at 1.4 microamps. If I shine a bright flashlight into the photodiode, I can get the voltage drop to decrease and currant to increase. If I hold the new LED approx 1" or less, voltage drops to near 0, and current increases to 40-50 microamps, and unit functions as normal. As soon as I move beyond the approx 1" approx, "ice full". Fully assembled, the LED and photodiode sit approx. 7" apart.
Attached is a rough sketch of "ice full circuit".
Any ideas? Seems either the LED isn't "powerful" enough, or the Photodiode isn't sensitive enough. I played around with the LED's limiting resistor until I had it up to approx. 100mA (max per spec sheet), and the Photodiode changed very little (up to around 10 microamps). This also made the 5V linear regulator a touch warm (specs out to 100 mA max), however the regulator stays at 5V throughout.
Thanks for your thoughts.