On my circuit I have a voltage detected (TC54) to detect when the level of the battery gets low. The output of this ic is high when there is enough battery, but it will be at battery voltage (12 or 15 volts). I am using a LM7805 to supply power for the microcontroller. Will feeding this high voltage level into the microcontroller cause damage? ( I would say yes to that). How can I read the signal out from the TC54? Would putting a large resistor in series with it solve the problem (1-5Meg)?
Here is the schematic for the design. The RB0 goes to the microcontroller. J2 is the input terminal on the board.
Electrical – How to read a high voltage logic signal with pic microcontroller
high voltagelogic-levelmicrocontroller
Related Solutions
I was hoping to be able to uniformly shift the voltage below 3V using diodes or a voltage divider but from a couple google searches it looks like current fluctuations would make that impossible.
That sounds like BS, do you have a source on that? A simple resistive voltage divider can be used to linearly scale down the voltage:
simulate this circuit – Schematic created using CircuitLab
This would drop the 4.2V maximum voltage down to 2.89V, well within the range of the input. The divider output has an impedance of 69KΩ, which should be low enough for the analog to digital converter but I could not find the ADC specs anywhere in order to make sure.
You need to buffer the signal before dividing it down. Op-amps are the usual way of doing that. Depending on the precision you need, an instrumentation op-amp costs a little more but has a lower offset voltage and tends to be the most linear over range.
The usual configuration is to connect the signal to the positive input of an op-amp, perhaps with a high value resistor for protection. The input of the op-amp is very high impedance. The output is then divided with resistors, and optionally fed into another op-amp buffer to avoid problems stemming from the impedance of the ADC.
The following schematic demonstrates a divide by 2:
Best Answer
Use Voltage Divider Circuit to read the battery level
If your PIC ADC support 3.3V then circuit will look like this one
If support 5V then use this
Note: If you want high accuracy choose right resistors for circuit, resistance value should be small as possible but same time it should not draw enough current that will effect battery. For more detail see this Link