0 - 5K Ohm to 0 - 5Volts

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evric
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0 - 5K Ohm to 0 - 5Volts

Post by evric »

When using a Kelly controller the input required from the Potbox is 0 - 5 Volts.
What is usually suggested is to take the standard PB-6 type potbox apart and connect to the third terminal, changing it from a rheostat into a potentiometer.
This is all well and good, except when you open the potbox case and measure the "Pot", the total resistance is about 20K Ohms. This is because the potbox is using 90 degrees or less of the full available pot travel(> 270 degrees).
If all three of the terminals were used, so as to try and emulate 0 - 5 Volts, the output would only be a quarter of the available voltage range of the pot. The effective output would then be 0 - 1.25V.
Maybe this is why Kelly controllers are not found to be very good - it could be just the input device we are using.

Has anyone come up with a conversion circuit that will convert 0 - 5 K Ohms to 0 - 5 Volts ?
Can we use a Hall Effect device in a potbox to directly output the required 0 - 5 Volts ?

Any thoughts ?

Ric ...
Last edited by evric on Tue, 17 Feb 2009, 05:44, edited 1 time in total.
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0 - 5K Ohm to 0 - 5Volts

Post by Johny »

I gather that you want 5 volts when the potbox is at 0 Ohms?
I.E. 5K to 0 Ohms equals 0 to 5 volts.

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0 - 5K Ohm to 0 - 5Volts

Post by evric »

Either way - it doesn't matter. The Kelly accepts 0-5Volts or 5-0Volts.
Last edited by evric on Tue, 17 Feb 2009, 05:57, edited 1 time in total.
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0 - 5K Ohm to 0 - 5Volts

Post by Johny »

Sorry - not trying to cause trouble - just clarifying. Image

So if you were to feed the top of your 20K potbox with 20 volts and place a 5.6 V Zener across the wiper to common (for safety) you would get 0 to 5V. That would need a DC to DC converter which means, if we are going to involve a DC to DC there is an easier option.

Option #2
---------
12V to 12V DC to DC converter - about 80 to 100mA device - about $10 $20.

Use the potbox as a 2 wire (unmodified) and run a 6.8K resistor from the DC converter output +12V to the potbox. If you want it dead accurate put a 220 Ohm is series with the 6.8K.


                                               |--------To controller
Vehicle                         ____   |
+12V-----|----------|+ ---|6.8K|---to potbox
               |DC to DC|       
Ground---|----------|- ------------to potbox
                                          |
                                           |----------To controller

Edit: Hey, you edited out the reason I said no trouble...
Last edited by Johny on Tue, 17 Feb 2009, 06:16, edited 1 time in total.

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0 - 5K Ohm to 0 - 5Volts

Post by Johny »

Hmmm. Does the Kelly put out any regulated lowish voltage for just this purpose?
Last edited by Johny on Tue, 17 Feb 2009, 06:18, edited 1 time in total.

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0 - 5K Ohm to 0 - 5Volts

Post by evric »

Yes - a 5V supply from the controller. This is, has to be isolated from the other supplies in the car. There is a 12V input (8 -30V) to the controller (isolated) which is common to the 5V o/p.
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0 - 5K Ohm to 0 - 5Volts

Post by evric »

Johny - It works out a little non-linear but it should work. Thanks. I should be able to use the 12V isolated output which I am using to power the controller and install some zener effect (using LEDs (LED's make great Zeners!) and a diode or two) to limit the output to 5V. Image is a bit scratchy and quick - sorry.

Ric...

Image
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0 - 5K Ohm to 0 - 5Volts

Post by Johny »

If you get picky later on you could substitute a PMP transistor and 3 resistors and make the pull-up a constant current source.
Do you actually have to provide a totally isolated 12V for the Kelly?
Does this isolated 12V have the same common as the potbox ground?
Sorry - I really don't know much about the Kelly.

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0 - 5K Ohm to 0 - 5Volts

Post by evric »

They actually tell you to common the pack 120V supply to the 12V supply. Of course I don't want to do this. I opted for an isolated supply (12V). This 12V supply has a common ground with the 5V/potbox.
I have now added the two green LEDs and three diodes as a 5V zener. Also I'm puting in a voltage sense to check if the pot goes open cct. to prevent the output going to 5V (Max. speed!) There is also a reverse speed control built in. The circuit is now update in previous post Ric...
Last edited by evric on Fri, 06 Mar 2009, 18:50, edited 1 time in total.
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0 - 5K Ohm to 0 - 5Volts

Post by evric »

The full updated 0-5kOhm to 0-5Volt converter circuit is now available in one of my previous posts. I also have a PDF version available from my website (Recommendations, Ideas & Parts page) with more explanation. Thanks to Johny for the original idea of the series 6.8K resistor.
Last edited by evric on Fri, 06 Mar 2009, 19:03, edited 1 time in total.
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