I have a hall-effect running on 12v that will be feeding pulses to a PicAxe datalogger. The PicAxe is of course a 5v device, so I need to get that 12v down to 5v. The hall is an open-collector and I was thinking to use a 5v zener to "clip" the pulse off.

When the hall is on it will sink all the current which will leave me low at the PicAxe input. In the "off" state the zener will take over and bring it up to 5v? The hall can only sink 20mA and I believe the standard 1N zeners like more than that, but low power BZX55C zeners can run on 5mA.

Might work. But I've been wrong before!

Any advice is as always .....

SP

 

Hello,

Perhaps you can use a circuit like the ones that are used as input of digital ports.
See schematic.
The resistor is th reduce the current at an "overflow" situation.

Greetings,
Bertus

 

I have a hall-effect running on 12v that will be feeding pulses to a PicAxe datalogger. The PicAxe is of course a 5v device, so I need to get that 12v down to 5v. The hall is an open-collector and I was thinking to use a 5v zener to "clip" the pulse off.

When the hall is on it will sink all the current which will leave me low at the PicAxe input. In the "off" state the zener will take over and bring it up to 5v? The hall can only sink 20mA and I believe the standard 1N zeners like more than that, but low power BZX55C zeners can run on 5mA.

Might work. But I've been wrong before!

Any advice is as always .....

SP

If it is open collector, you will need a pullup resistor on the output. You can simply connect the other end of the resistor to +5V. You won't need a zener. Check the datasheet, but 10k should work.