No problem David, I appreciate your response... Here's the challenges I've been having.
I tried to put a 3.3V zener on the voltage divider but I found it would leak enough current that it messed up the operation of the V divider. After some research I read that low voltage zeners have significant leakage.
Then I went looking for a Transorb and most everything i read says they are not well suited for logic level voltages. I could find no example of Transorb being used as logic level protection.
I ended up doing something odd... I placed an LED between the 3.3V zener and ground. The added resistance provided by the led to the back side of the zenner causes it to hold and allow my V divider to work properly. When voltage at the divider did exceed 3.3 volts it does open. The led does not light as there is not enough current. But it does pass the current overflow from the zener...
I cranked my signal power all the way up to 40V and the voltage in the divider never went over 3.5V... And down in normal 12-14V signal range the divider is working as expected giving me 2.8V at a 14V signal...
I was reading elsewhere to do the following to protect an adc pin... Set up your V-divider and simply place a 150K resistor from the divider to the ADC pin. The author says that although the divider voltage could go well above the pin limit, that the current would never be enough to hurt the pin because of the 150K resistor...
I do not know enough about what really would hurt the adc pin on the mbed... Whether it's just any high voltage or an ecessive current of anything > X?...
If I could protect the adc pin with the 150K resistor that is what I would choose over what I'm doing now.
Tim
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Hi All,
Anyone set up the mbed to read a voltage source 0-14V and convert it to a 1-100% signal measurement? I want to do it the simplest way possible... Voltage divider , External IC... etc...
I suspect the analog in pin would be used in the end?
Thanks
Tim