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Q: 5V<->12V level conversion

A

Adam Bradley

I'm after some validation of this circuit ->
http://members.optushome.com.au/adambradley/electronics/LevelConverter/cnv.j
pg

I'm after a way of sending/receiving from my car ECU a 12V digital signal
using a uController (AVR).

A kind sole presented the above circuit. Based on the labelling, to transmit
from the car (12V) to uController(5V), place 12V (or 0V) on the collector of
Q1 (labelled K line) and read on Tx.

To transmit from the uController, place 5V (or 0V) on Rx and read
from the K line.

I've also discovered placing 5V (or 0V) on the emitter of Q1
(labelled Tx) works! This freaks me out! Why does this work ?

Anyone got any general suggesions as to whether this is a good
approach. Also, if I want to include optoisolate this circuit (in
both directions) how would I go about doing this given a single line carries
Tx and Rx information?

Thanks in advance!

Adam
 
A

Adam Bradley

I've uploaded a couple of images of my schematic in which a TTL high and low
(5v and GND) is injected into the circuit.

Once again the two files are in
http://groups.yahoo.com/group/opendiag/files/AJB/

and called

5V connected to TTL Tx.jpg
5V disconnected from TTL Tx.jpg

The multimeter reading is taken from the K line.

Any ideas how this works?
:)

Adam
 
K

Ken Taylor

The groups link requires a login/password, and the other links previously
used don't work ("404").

Ken
 
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