nib1980
|
| posted on 23/8/07 at 07:44 AM |
|
|
Pull up resistors for hall effect sensor - HELP
Hi all,
following on from my previous threads about the speedo calibration, i got intouch with the speedo healer people, very helpful and very useful. They
have said based on the signals I'm measureing I may need a "pull up resistor" to amplify the signal.
Now I've done a bit of research, electris is not my strongpoint, and electronics certainly isn't, but I think if id do the following I can
amplify the signal suitable for the speeohealer to use.
Please can someone comment before i blow somehting up!.
Many thanks
[img][/img]
|
|
|
|
|
jkarran
|
| posted on 23/8/07 at 08:20 AM |
|
|
Without knowing that specific sensor I can't be certain. However, it won't harm your Speedohealer. Assuming the sensor has a transistor
pulldown output of some kind, it's in the right place an is very unlikely to harm the sensor. Looks right to me.
jk (electronic engineer )
|
|
|
nib1980
|
| posted on 23/8/07 at 08:43 AM |
|
|
the transducer is this one
http://www.merlinmotorsport.co.uk/p1321/TRANSDUCER-M18X1.5/product_info.html?osCsid=051a070663a28b21893dface1cf5e2e1
I've emailed them for more detailed specs than it came with
|
|
|
Bob C
|
| posted on 23/8/07 at 09:27 AM |
|
|
All the hall effect sensors I've seen have an active pull down but rely on a resistor to pull up.
The disadvantage of pulling up to 12V is that you then have a 12V signal going into your 5V or 3.3V electronics. This could cause damage but is more
likely to work fine. You might get issues with the 12V pullup actually pulling up the local 5V or 3.3V supply - can cause analog errors.
Best solution is to pullup to the logic supply - if the dash is designed for hall sensor there might be a jumper or component location on board for
this. Other possibilities are to use 2 pullup resistors in series as a potential divider or 1 resistor and a zener....
If you're stuck get someone with a bit of experience to help you, it's not really practical to debug these things in a forum...
Bob
|
|
|
02GF74
|
| posted on 23/8/07 at 09:29 AM |
|
|
^^^ that sounds reasonable but without knowing the spec of the transducer cannot it will workj 100%.
You may find the the low value is a higher voltage so the healer may not like it.
Easy enough to tet though, if you have dvm.
|
|
|
wilkingj
|
| posted on 23/8/07 at 09:29 AM |
|
|
Well at least you acknowlege your shortcomings in the electronics world.
You are wise to ask first! Its also cheaper.
I do not know the answer.
I would not take their word over the phone.
I would expect them to Email me a drawing, or point to one on the web, or give detailed written instructions.
Only then will you be clear about the way forward. and you would also have a comeback if it failed disasterously.
I can't see how a pull up resistor will "amplify" the signal. However, if it is a pulsed type output it could clean up the pulses by
ensuring the signal wilre is always at 12volts, and only the sensor would lower / pull down the voltage.
Who gave you the value of 4k7 Ohms?. Its probably right, but will depend on the internals of the sensor etc. I am not saying its wrong, just to check
and double check.
Hope all goes well.
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
|
|
|
nib1980
|
| posted on 23/8/07 at 09:35 AM |
|
|
this was the response i got from the speedo healer people
Hello Neil,
Thank you for your email.
You need an SH with extended calibration range (SHv3.0-C8) and an Universal harness kit.
You can order it in the UK from sales@bikersdiscountstore.co.uk
Hall effect sensors require an external pull-up resistor (e.g. 4.7K) to +5V or to +12V.
If the sensor does not send the pulses when hooked up to the speedometer, it means this pull-up resistor is not in your speedometer and should be
added manually.
In this case we need to make a custom SH which has this extra resistor on board.
I can measure the sender pulsing but only the low voltages, and there is no movement on the speedo, So I'm guessing I need this extra resistor
in the speedo healer.
Lookslike i need to find a local expert, and i think i know just the person.
|
|
|
02GF74
|
| posted on 23/8/07 at 11:09 AM |
|
|
quote:
Originally posted by wilkingj
I can't see how a pull up resistor will "amplify" the signal.
If it is open-collector output; the change in signal will be very low - the pull up is required - not striclty amplifaction as such.
... but then as ^^^ and I said earlier, it very much depends on the spec of the sensor so we can only speculate.
|
|
|
