nib1980
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| posted on 23/8/07 at 07:57 PM |
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Resistor check (from earlier HELP)
Hi All
Following on from this thread
http://www.locostbuilders.co.uk/viewthread.php?tid=72839
I spoke to an electronic guy at work who got me a 4K7 resistor to try, and it boosted the voltage to 2.2 from 0.22. based on this i did some basic
calculations and I think I need eith the following 17K1 or 25K depending on if I want 8v or 12v.
Does my logic seem sound?
Many thanks
[img][/img]
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NeilP
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| posted on 23/8/07 at 08:42 PM |
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Think so - In terms of the power rating of the resistor you need to used current squared multiplied by resistance...
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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paulf
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| posted on 23/8/07 at 08:42 PM |
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Neil
It wont make any difference what the value is when checking with a DVM as it is just providing a link to the 12v supply, when the sensor is not giving
an output to earth. It just needs to be big enough not to overload the output of the sensor as when the sensor operates it is now switching the 12v +
supply to earth via the resistor and therfore providing the low side of the signal pulse.
I have an inductive sensor that you can try if you like it will give a positive 12v pulse.
Paul.
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nib1980
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| posted on 23/8/07 at 08:52 PM |
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HI Paul,
you Have U2U
I'm not sure what the rating of the sensor is I'm guessing it can't be measured? I'm thining I can try uping the resistors
until something and if it doesn't go pop then I may be OK?
But I think I may take you up on that offer. I take it it will be monuted on the diff to measure the prop rotations?
and it will still need to be fed through a speedo healer?
regards Neil
quote:
Originally posted by paulf
Neil
It wont make any difference what the value is when checking with a DVM as it is just providing a link to the 12v supply, when the sensor is not giving
an output to earth. It just needs to be big enough not to overload the output of the sensor as when the sensor operates it is now switching the 12v +
supply to earth via the resistor and therfore providing the low side of the signal pulse.
I have an inductive sensor that you can try if you like it will give a positive 12v pulse.
Paul.
[Edited on 23/8/07 by nib1980]
[Edited on 23/8/07 by nib1980]
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02GF74
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| posted on 24/8/07 at 08:16 AM |
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I won't comment on ^^^^ but let's just say I don't wholly agree.
Again we are making guesses since we do not know the details for the ouptu stage.
Here is my take - a guess - so may not be right. It would help if you do a couple of tests and supply mnore info.
The voltages you gave in first post we 0 more or less and 0.2.
I recall from my electronics days that when a transistor is fully on, the output drops to 0.2 V.
Now I am guessing your output stage is open collector or something like that.
So with your 4.7 K pull up resistor, can you measure on voltage - sensor is next to magent and off voltage - sensor is away from magnet.
If you are seeing 2 something volts when the sensor is on, then it does not point to open collector.
Now I will be making my own sensor and have been playing round with hall sensors. There is an output stage - I need to look in my notes - and I seem
to recall that it has 2 transistros , one switched when sensor is on, the other switch on when snetor is off so I had to use two resitors, one as you
have and the other to 0 V.
If I remember, I will look at my circuit.
.... but it still seems we are guessing - you could try a 10 K and 2 K reistor and supply us woth the voltage when the sensor is off and when it is on
- that may give us some clues.
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