#DM13A and Dual LED Korries

1 messages · Page 1 of 1 (latest)

spiral sail
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Hi! I have been experimenting with use of DM13A for quite a while now and understand how they work but I am still quite a novice in electronics. I designed my own DM13A boards and ordered them from JLCPCB and they work a treat (I've added filtering, some pullups etc too). One of them is going to be used with 737DIYSIM 318 Korries PCB's which houses two 6x6x7 tacticle LED white switches. Here is where my trouble comes - I am stuck at selecting REXT resistor value. Looking at the Schematic of these, Karl normally connects one of the PCB's to 5v/Arduino via 120ohm resistor. How does that work in terms of current? I believe they are wired in parallel so does that mean LED PCB get's total of 20mA and each of LED's get's around 10mA if 120ohm is used? Should I in this case aim for 20mA per DM13A out channel? I've been experimenting with different sizes and at moment I've got a 1680ohm (1k+680) and channel output is approx. 33mA. But all this is guess work at moment, and I want to know how to calculate it properly every time and if this below calculation will give me 20mA at channel:

REXT = (VREXT x M) / IOUT
M (from datasheet for 20mA) = 46.6
VREXT (from datasheet) = 1.2
IOUT (desired channel current) = 20

REXT = (1.2*46.6) / 20
REXT = 55.92 / 20
REXT = 2.796

Thanks!

737_YOKE_CONTROL_HEAD_single_2020-Oct-31.png
spiral sail
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Also, something strange that I just noticed and its absolutely baffling. I have this all connected on my desk with no external P/S. Two Korries via Arduino 5V and DM13A board I've done. Nothing special. It's been stable for 30mins constantly on right now and not a single flick. As soon I got up they both switched off and turned back on after few secs. I thought strange.. But then I went away, came back and tried to sit down and they switched off again. ITS not coincidence. I went and tried to get up and down probably around 100 times and nearly everything single time they switch off for few secs. It's not to do with vibrations as I shaked the board, arduino, usb, korries and dm13a boards and nothing happens. Its only when I try to get up and sit down. How is this possible? I've not got any metal in me from operations or pacemaker etc.

spiral sail
digital plank
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Rext[kOhm] = Vrext[V] x M / Iout[mA]

Rext = 1.2 x M / 20 = 0.06 × M

For M = 46.6 you would need a 2.7 kOhm external resistor (mathematically 2.796, but 2.7 is the closest value)

#

If you are driving the LEDs with an LED driver chip you don't need a current limiting resistor. The driver chip limits the current.

Driving two LEDs from one DM13A channel will not guarantee both to be equally bright. One may have a slightly higher forward voltage than the other leading to a significant difference in brightness...

digital plank
spiral sail
# digital plank I'm not sure I understand what you're trying to do with this circuit

The circuit on picture is Karl's from 737diysim PCB boards for 318 Korries replicas. They use 2 x 6x6x7 led tacticle switches per pcb and I assume that when run from Arduino Karl uses inline 120ohm resistor to give them the required current. I am trying to achieve that same current from dm13a. I was trying to verify that my 2.796 calculation is correct and also what exactly does M represent.

digital plank
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In the circuit you posted, I don't see any connection between the buttons and the arduino that mobiflight can use. The 2 additional LEDs are confusing, what are you trying to achieve with them?

This circuit diagram from the 318 V2 page seems like it would work.

Concerning the resistor:
Whatever the resistor value, it will turn on the LEDs constantly. I'm not sure if this is needed. I believe it may be a mix-up from another Korry with constantly backlit text AND an annunciation light. But I might be wrong.

I'm off to work now, but if you'd like, I can sketch something up this evening that I think will work with a DM13A driver.

image0.jpg
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M seems to be an arbitrary number the manufacturer has determined in tests

digital plank
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Aaah, hang on, I think I understand what Karl is doing here... the 5Vin with resistor connection is used as a test function.

Apologies for the confusion.

#

I think it would be wise to achieve this test function in software. The SIM will do this anyways. That will simplify the circuit considerably (no reverse current protection diodes necessary, no resistor necessary, just buttons with LEDs)

If the SIM itself doesn't provide this function for whatever reason, it is still achievable in mobiflight.

I will draw up a circuit diagram this evening showing what I'm talking about.

digital plank
spiral sail
# digital plank Are you planning on using the PCBs sold by Karl or are you planning on making yo...

It's actually for both. My MIP is based on Karl's 737 SS design 1:1 using all his parts. I am not using push to test though and had the Korries already working but I believe I had them at too high current. If there was a solution for push to test through software id be really interested in this! That's why now I am now using 2.7k ohm resistor. (I just went for it and installed one and all is well)

For the rest of Korries I actually made my own PCBs with whute SMD pre soldered. They work quite well and are 20ma rated too so I'm just gonna stick to 2.7k for the rest of the build. I have attached some pictures of the final results. Low Pressure is mine and INOP is from Karl.

20251129_153730.jpg 20251129_161228.jpg 20251129_162505.jpg 20251130_002141.jpg
spiral sail
digital plank
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For the rest of Korries I actually made my own PCBs with whute SMD pre soldered.

So without a pushbutton?

spiral sail
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Yes, I figured out I don't need the push to test function as it overcomplicated the whole idea of trying to keep number of arduinos to minimum and significantly increased cost/time of jlcpcb assembly.

digital plank
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If you don't need them in Sim I think thats a great idea!

pulsar saffron
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push to test, make a mobiflight variable for that. Then on each led config bring the test-variable as config-reference (placeholder # as an example here and make a Transform $ or #

digital plank