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Hello all. I'm running a 12F683 at 3.3V. One of the GPIO's is connected to a place in a circuit that rises to only 1.2V when it's activated. Is this enough voltage to reliably support the code "if gpio.X = 1 then..." or does it need higher voltage to detect it consistently? Thank you.
Hi,
Looking at page 121 in the datasheet it says that when Vdd is between 2.0V and 4.5V a TTL input is considered high when the voltage on the pin is 0.25*Vdd+0.8V. With a 3.3V supply this equals 1.625V so 1.2V is not guaranteed to be interpreted as a logic 1. For a schmitt trigger input the number is 0.8Vdd which for 3.3V is 2.64V so even "worse" in your case.
/Henrik.
Thank you Henrik. I need to find another way to detect when the circuit is active.
Just use a simple transistor buffer.
Pullup resistor on I/O-pin, NPN transistor pulling I/O-pin to GND when the 1.2V signal drives a small current into the transitors base.
/Henrik.
Unfortunately the circuit board is already manufactured with a pull down resistor network. The switch that activates the circuit which I'm trying to detect goes to ground when pushed. True, I can use an inverter but it needs to be a very simple hook-up. Attach B+, B-, one wire output and one wire detect. I'll probe around more today to see if there's another way around this. Again thank you Henrik.
Just use the ADC to measure the voltage on the pin and decide in software what is a high and what is a low.
if your pin is an analog pin, use the a/d mode to make a thresh-hold that works.......
(beat me by 2 minutes)
Thank you everyone. I found a spot that goes up to a full 3V when the circuit is activated but is a difficult connection to make. I'm going to use the ADC solution as this connection is much faster and easier.