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  #1  
Old 10-10-2018, 11:32 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 77
Question KY 97A - PWM dimmer?

This may be way too deep, but I'll throw it out for someone... Looking at swapping an older King 197 Comm for a free KY 97A (known good too).

Looking at the pin out differences...

Looks like the old radio had a built in dim sensor, while the KY 97A has pin A "Dim Select" and pin B for +14 V lighting input. So, OK, cool it can track panel dimmer lighting. However... I don't have a simple rheostat, I have a PWM dimmer circuit. [Buzzword alert: PWM = pulse width modulation, basically the dimmer dims by turning on and off many times per second, varying the on vs. off time to control brightness.] Similar to https://www.aircraftspruce.com/catal.../pwmdimmer.php - but actually home built. Has anyone used a PWM dimmer with a KY 97A?

I'd hate to put this in and discover I can't get the dimming to work.

thanks in advance for helpful info.

-Bryan
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Last edited by blaplante : 10-10-2018 at 11:33 PM. Reason: typo
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  #2  
Old 10-11-2018, 01:43 AM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
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A simple RC circuit can change the PWM to average DC. E.g., line from PWM to resistor to capacitor (other side to ground) and King dimmer input.
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  #3  
Old 10-11-2018, 02:52 AM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by BobTurner View Post
A simple RC circuit can change the PWM to average DC. E.g., line from PWM to resistor to capacitor (other side to ground) and King dimmer input.
Yes, but the KY 97A is pre-LED so the incandescent bulb should act the same as the RC circuit shouldn't it?
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  #4  
Old 10-11-2018, 01:07 PM
BobTurner BobTurner is offline
 
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Originally Posted by az_gila View Post
Yes, but the KY 97A is pre-LED so the incandescent bulb should act the same as the RC circuit shouldn't it?
If the dimmer circuit directly drives the bulb, yes. If there’s some circuit in between, can’t say. Shouldn’t hurt to just try.
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  #5  
Old 10-11-2018, 02:00 PM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by BobTurner View Post
If the dimmer circuit directly drives the bulb, yes. If there’s some circuit in between, can’t say. Shouldn’t hurt to just try.
Yes, you are correct, there is quite a bit of circuitry involved... and an amazing total discrete component count, showing the pre-digital integration technology of the era...

Schematics here - https://opendevices.ru/wp-content/up...ell-ky-97a.pdf
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EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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