falco_femoralis
Well-known member
Can I use, for example, red LED's instead? Asking for a friend
On the Arachnid PCB, do the 914's have to be 914's?
- Thread starter falco_femoralis
- Start date
Hmm seems like it may not work, not sure. Should be able to try it…
Red LEDs are typically around 1.8v forward voltage, compared to around 0.5-0.7 for the 914s. If you drop 3.3V by 1.8v, you get less than half of 3.3, and I’d expect the fv-1 inputs to go high or low compared to the halfway point 1.65).
I also know leds are not as robust to high reverse voltages or reverse surges compared to schotkys, but I don’t think you’d have any problems since 3.3V would be the max (online says red leds can have 5v breakdown reverse voltage). So that’s probably ok, more concerned bout the first paragraph
Red LEDs are typically around 1.8v forward voltage, compared to around 0.5-0.7 for the 914s. If you drop 3.3V by 1.8v, you get less than half of 3.3, and I’d expect the fv-1 inputs to go high or low compared to the halfway point 1.65).
I also know leds are not as robust to high reverse voltages or reverse surges compared to schotkys, but I don’t think you’d have any problems since 3.3V would be the max (online says red leds can have 5v breakdown reverse voltage). So that’s probably ok, more concerned bout the first paragraph
On the other hand, the 100ks would act as the LED resistors, making the current draw very low. The fv-1 pins themselves should have very high impedance. The LEDs would probably be quite dim.
There is a relationship (datasheet graph) between forward current and forward voltage, so maybe with low current, the voltage drop would be lower and not dip below the 1.65v. But it’d be cutting it close.
There is a relationship (datasheet graph) between forward current and forward voltage, so maybe with low current, the voltage drop would be lower and not dip below the 1.65v. But it’d be cutting it close.
40-70 mA for the FV1 alone though ..
I'd probably spec up the regulator to be safe. Plenty of 200mA out there for a few cents more. I suspect the analog signals of 0.5V in the datasheet would cover the switching so there probably enough voltage left after the LEDs to work.
I'd probably spec up the regulator to be safe. Plenty of 200mA out there for a few cents more. I suspect the analog signals of 0.5V in the datasheet would cover the switching so there probably enough voltage left after the LEDs to work.
Ah. Yeah it’s confusing, idk. Since it’s in the Max Ratings section, I take that to be the max you can feed pin 1-2 without damaging the chip. If AVDD is 3.3V, make sure the signal in doesn’t go past 3.8v.
A friend had an EQD Afterneath that was acting up, sometimes worked fine, other times no wet. Turns out pin 16 was just… floating. Noise interference could influence into the high or low state. I Tacked on a 10k resistor to gnd and never an issue since. Though, I didn’t determine that 1.65v was actually the threshold.
For the original question, give it a try haha. If it does work, I don’t expect them to be bright.
A friend had an EQD Afterneath that was acting up, sometimes worked fine, other times no wet. Turns out pin 16 was just… floating. Noise interference could influence into the high or low state. I Tacked on a 10k resistor to gnd and never an issue since. Though, I didn’t determine that 1.65v was actually the threshold.
For the original question, give it a try haha. If it does work, I don’t expect them to be bright.
