Easy OKR-T VV mod

[bstedh]

OK - More resistance means less voltage?
Why would you want max resistance with no variance?
That means not adjustable right? Why have a pot at all?
Why is there a resistor on the pot? Does that change the range?

With this regulator the lower the resistance the higher the voltage output.

I don't think you would ever want max resistance other than in some specialized circuit.

I only use the variable of one side. You could tie it in for protection but if it's broke its broke

The ohms range for the regulator is 200ohms for around 6V and 450ohms for around 3V so you want a minimum of 200ohms hence the resistor attached to the variable giving you an operating range from 200ohm to 400ohm or 450ohm depending on the value of the variable resistor you choose. Basically the resistor sets the lower end of your range.

Here is a pic of the table I used to figure out the resistance needed for this regulator. The 200ohm variable was not in stock when I ordered so I had to figure it with 500ohm hence the difference in circuit design from what is posted here.

Edit: I worded the values wrong but the table will make that clear =]
Edit: fixed

 

[VpnDrgn]

I think I understand ( prolly not ).
If I got it right, I should be able to use this pot and wouldn't need the resistor, right?
Digi-Key - P16NP-22K-ND (Manufacturer - P16NP223MAB15)

 

[bstedh]

thats a 22K or 22000ohm resistor so it would not work. You will always need the single resistor to set you low end resistance as a variable goes from 0ohms to what ever it is rated at.

Edit: Read the spec sheet for your regulator to determine the resistance range you will need for the trimmer circuit. You then select a standard resistor that matches the highest voltage you want. Then figure the resistance you need for the lowest voltage you want and subtract your first resistor value from that to determine the ohms of the variable you will need.

 

[VpnDrgn]

So the resistor sets the low end / the pot sets the high end?

According to this spec sheet, the chart shows the 47 ohm having a max voltage of 6.85,
so that would be my high end? http://www.vishay.com/doc?51036

 

[bstedh]

So the resistor sets the low end / the pot sets the high end?

According to this spec sheet, the chart shows the 47 ohm having a max voltage of 6.85,
so that would be my high end? http://www.vishay.com/doc?51036

You are not pushing the voltage through these as they are just giving a ground reference to the regulator to set it's voltage level so a high wattage potentiometer is not needed. I do think you are getting the idea however but I think I messed up my description a little.

The standard resistor sets the [low ohm/high voltage] limit and the variable resistor adjusts from that point to the [high ohm/low voltage] limit. Hope that clears it up a little =]

Here is a 470 ohm version of that pot that is a little closer to what you could use without the standard resistor. You would not have the high limit without the standard resistor however so your regulator would be able to go all the way to it's maximum possible voltage. These Pots are overkill however unless you like the look and feel of them =]
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P16NP-470-ND

Here is the formula for figureing out the resistance levels vs. voltage for the OKR-T regulator. RTRIM (k) = _____________
(VOUT – 0.591)

Guess it doesn't copy and paste very well... I will post an image of it shortly..

 

[bstedh]

I dug up the spread sheet I used with the formula

Resistance=(1.182/(Voltage-0.591))*1000

ohms - Vout
444.528 - 3.25
406.3252 - 3.5
374.169 - 3.75
346.7292 - 4
323.0391 - 4.25
302.3791 - 4.5
284.2029 - 4.75
268.088 - 5
253.7025 - 5.25
240.7822 - 5.5
229.1142 - 5.75
218.5247 - 6

So at 444ohms you get 3.25V out of the regulator
At 218 ohms you get 6V out.

So if you wanted non variable you would use a single resistor at the the correct ohms for the voltage you would want. I use the standard 200ohm resistor so that the voltage can never go higher than 6V. then with a 200ohm variable in series you can go from 6V down to about 3.5V.

 

[Rockproof]

Very nice illustration bstedh. Definitely one I can follow.

 

[bstedh]

Very nice illustration bstedh. Definitely one I can follow.

Thanks a lot. I appreciate it.

 

[VpnDrgn]

Thanks Bstedh,
I do like the looks, but the main thing is that it is panel mounted. I won't have to worry about kludging together a stem and knob.
It should give me a little more flexibility in where I can mount the knob on the outside in relation to where I mount the board
on the inside. I don't really have the knowledge yet to be putting together my own circuits, but the pre-assembled boards are
so big and the mounted pot severely limits where the board can be mounted inside the mod.

I have the four different 4050 booster chips. Would this pot be the one to use with the 4050 booster in Breaktru's configuration?

 

[bstedh]

I haven't really looked into to buck/boost circuit yet. You would have to ask one of the guru's that play around with them. I have only perused the info on them and don't have a good understanding of the needs for that chip yet and probably won't until I try to build one =] I'm the type that has to learn by trying and failing several times until I get it right...

 

[bstedh]

Also if you look at my VV weller post listed in the OP just above the diagram you will see how I remotely mounted mine. With the other boards you can relocate the trimmer by removing it from the board and extending it with some wires if needed.

 

[bstedh]

Do you have a link to the spec sheet for that circuit? I can take a look and see what it seems to require quickly...

 

[VpnDrgn]

You can find it here and the spec sheet is here
You can also order a sample of each.

Breaktru did a booster mod called the .44 mini booster.

Not sure if he figured it out, but his diagram shows how to get the booster voltage out below the spec'd 5V's.

 

[bstedh]

Reading...... (may take awhile) =]

He has a diagram like mine =]

Looks like you need a 100K variable.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P16NP-100K-ND

I would read through his whole thread and make sure you have a good understanding of the build before ordering parts however.

 

[VpnDrgn]

I found a step-up-step-down regulator on a robot website that someone else had linked to for a batt.
It is perfect for our needs and is tiny and cheap. Only problem is a low amp rating. I contacted the company
and they are gonna talk to the mnf and see what they can come up with.

 

[bstedh]

It looks like that diagram is linked on another forum

.44 mini Booster Box Mod Variable Voltage

 

[Dalton63841]

Reading...... (may take awhile) =]

He has a diagram like mine =]

Looks like you need a 100K variable.
Digi-Key - P16NP-100K-ND (Manufacturer - P16NP104MAB15)

I would read through his whole thread and make sure you have a good understanding of the build before ordering parts however.

I have seen the Tantalum CAPS on a few diagrams and when looking for them, I cannot find them. I can find 100uF CAPS of several kinds, but not the Tantalum. Does it HAVE to be that kind, or what in general should I be looking at?

 

[bstedh]

The big thing that has kept me away from the buck/boost option is all the other components that are needed.

 

[bstedh]

Digi-Key

I have seen the Tantalum CAPS on a few diagrams and when looking for them, I cannot find them. I can find 100uF CAPS of several kinds, but not the Tantalum. Does it HAVE to be that kind, or what in general should I be looking at?

oops that link didn't work

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=478-1845-ND

just search Tantalum on digi key's site and then go through the filters for the voltage and capacitance you need.

 

[Scubabatdan]

The big knob... 100k:
Digi-Key - P16NP-100K-ND (Manufacturer - P16NP104MAB15)
Dan