DC Voltage Conversion for Pulse Output Device

I’m hoping someone can have some sympathy on me and provide a little guidance. :slight_smile:

I have a device with a pulse output that I’d like to count using the imp. The device outputs 12 Volts DC for 250ms capable of providing 50mA. I come from a software background and so I’m not sure the best way to convert this 12V pulse down to 3.3V for the imp. I’ve done some research on voltage regulators, voltage dividers, etc. but if someone could give me some guidance and do a little hand holding for me I’d greatly appreciate it!

There’s an app note from TI discussing interfacing the 3V MSP430 to 5V or higher circuits. Take a look at section 3 which goes into a lot of detail about the various options; resistor divider, transistor buffer, op-amp and more (and with lots of equations!)

Interfacing the 3-V MSP430 to 5-V Circuits

Its not exactly hand-holding but I find that working it out myself sometimes means I might remember it in the future :slight_smile:

Personally I’d use a zener diode to clamp the voltage.

  1. The grounds of the imp and the device have to be connected together, so there’s a common reference. If you’re powering an April from the device (as you could if it has 12v available) you should be fine.

  2. Take the signal, run it through a 10k resistor, and then to the top (cathode) of the zener, then to the imp pin. Use a 3v0 or 3v3 zener. The diode will clamp the maximum voltage the imp sees and the resistor will burn off the excess.

See the bottom diagram here http://www.daycounter.com/Circuits/Level-Translators/Level-Translators.phtml …for an example.

Obviously, check it with a meter before you attach it to the imp but that should work fine.