Simple way for separate trim pots.

Various circuit diagrams
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tiptipflyer
Posts: 141
Joined: 16 Feb 2018, 22:49
Location: Germany

Simple way for separate trim pots.

Post by tiptipflyer » 25 Feb 2018, 09:56

Works great and easy to install.
Trimpoti.jpg
Frank
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jmendoza
Posts: 70
Joined: 18 Feb 2018, 23:07

Re: Simple way for separate trim pots.

Post by jmendoza » 07 Mar 2018, 21:57

Thanks for that. You must have been reading our minds here in California! :o

We were just getting ready to add Phils DIY-More 7ch+ S/C to a Kraft with separate trims. This will save us, and Phil some time as I was going to e-mail him about this and he is busy enough without my silly questions. :D In fact, our Kraft trims are already wired per your diagram, using 5K stick, and 1K trim pots, so my question to Phil was going to be if we could wire them as is to the analog inputs A0-3.

Jay

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_AL_
Posts: 67
Joined: 17 Feb 2018, 01:09

Re: Simple way for separate trim pots.

Post by _AL_ » 10 Mar 2018, 22:57

I used the attached on my 78 Kraft.
I can't see what the stick pots or the trim pots are rated (they are the original ones from the radio) but with a 47k resistor I got no measurable change in voltage so with a bit of testing I settled on 4.7k resistor between the stick & trim which gave me about 10% of the total throw (in volts) in trim adjustment.
I finally got the radio fired up last night & found 10% is too much so I'll work it out again at 5% which should be about right.

Al
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Tobe
Posts: 70
Joined: 16 Feb 2018, 06:19

Re: Simple way for separate trim pots.

Post by Tobe » 11 Mar 2018, 16:01

Just remember that low rate affects trim also! That way I use a trimpot in the between

FBMinis
Posts: 35
Joined: 25 Feb 2018, 17:59

Re: Simple way for separate trim pots.

Post by FBMinis » 14 Mar 2018, 22:15

_AL_ wrote:
10 Mar 2018, 22:57
I used the attached on my 78 Kraft.
I can't see what the stick pots or the trim pots are rated (they are the original ones from the radio) but with a 47k resistor I got no measurable change in voltage so with a bit of testing I settled on 4.7k resistor between the stick & trim which gave me about 10% of the total throw (in volts) in trim adjustment.
I finally got the radio fired up last night & found 10% is too much so I'll work it out again at 5% which should be about right.

Al
I found a circuit similar to yours which solves the excess sensitivity by adding a couple of 1.5K resistors:

http://www.norcim-rc.club/Radio3.htm

http://tinyurl.com/y7hbhuhk (Falstad circuit simulation)

You can replace 1.5K with 2.2K, a more common value, for even less trim sensitivity.

FBMinis
Posts: 35
Joined: 25 Feb 2018, 17:59

Re: Simple way for separate trim pots.

Post by FBMinis » 20 Mar 2018, 19:28

NE5044 encoder IC typical input adjustments circuits:
5044.jpg
S-7 Basic Control Hookups.jpg
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