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Aug 08, 2002, 07:45 AM
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Add Channel switch


Hi. I am wondering if there is any way to add 1 or more channels to my 4 channel radio to use for other stuff like an on off switch for lights. I can't afford a new radio.
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Aug 08, 2002, 09:28 AM
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Maybe. What transmitter do you have?
Aug 08, 2002, 10:28 AM
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I use a Focus 4
Aug 08, 2002, 12:28 PM
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I think you are in luck The old Focus 4 used the NE5044 encoder, so up to seven channels can be supported. Of course you need to be prepared to do a little hacking. This is not a job for an entry level tech either.

Open up the case and remove the screws to the big board on the right. Find the 16-pin chip marked NE5044. Pins 5, 6, and 7 are R/C channels 5 thru 7. They are probably grounded or tied to VCC.

If you wish to use channel 5 as a switched channel, then your task is easy. A SPDT switch and a 330 ohm resistor will be all you need. If you need more help, just tell me what you find and I should be able to offer specific instructions. Be sure to post a photo of the top and bottom PCB area near pins 5-7.

Since the Focus series was also offered in a six channel configuration, the circuit board probably has unused PCB pads for you to use. Better yet, borrow a Focus-6 and see what they did inside it.

Regards,
Mr. RC-CAM
www.rc-cam.com
Aug 08, 2002, 02:11 PM
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Here are 2 photos
I don't know which pins are which numbers
Last edited by mechpb; Aug 08, 2002 at 02:17 PM.
Aug 08, 2002, 02:19 PM
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the second
Aug 08, 2002, 02:55 PM
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So far so good. However, the solder side view does not readily indicate the orientation of the NE5044. I need to see what is soldered to those "unused" pins.

Using the retouched photo below, where are pins 5, 6, and 7 on the solder side?

Using a voltmeter, what voltage do you read on them when the Tx is on? Use pin 8 for ground. Be careful, or you will be very sorry.
Last edited by Mr.RC-CAM; Aug 08, 2002 at 02:57 PM.
Aug 08, 2002, 03:02 PM
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Oh, now I {think} I see how the chip is positioned. Unless my compass is mixed up, pins 5, 6, and 7 are connected to the ground (pin 8) by the PCB's copper trace. Is that what is going on in that area?

If so, this mod will require a little trace cutting and jumping. Are you up to it? Have you done this sort of thing before?

Regards,
Mr. RC-CAM
www.rc-cam.com
Last edited by Mr.RC-CAM; Aug 08, 2002 at 03:10 PM.
Aug 08, 2002, 03:18 PM
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5 6 and 7 all have 0 voltage when grounded through pin 8 and yes they are all connected throught the trace.

Sure...I'm up to it!
Aug 08, 2002, 04:53 PM
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Alrighty then ...


You'll need a temperature controlled soldering iron (30-40 watts) and a anti-static work area.

To enable RC channel five you must first isolate NE5044 pin 5 from the grounded copper trace. Remove the battery from the Tx first!

(1) The photo below shows pin 5, highlighted in green.

(2) Using a sharp X-Acto knife, cut pin 5 away from the two places indicated in Red. When you are done, NOTHING should be connected to pin 5. Use a ohmmeter and verify that the "shorted" connection to pin 8 is several hundred ohms or higher.

(3) Refer to the Yellow line, which represents a jumper wire. Using 26-32 AWG insulated wire, connect the freed capacitor to pin 8 (connection was lost in the cut step). Do not short anything out. Do not use so much heat that you totally liberate the SMT style cap.

(4) Now solder a .01uF cap across pins 5 (Ch-5) and pin 8 (ground). The cap is not shown in photo.

Now you have a channel five input that you can use. Your choices are to add a variable pot (trim knob) or a toggle switch (flaps or gear).

(4) For a Trim function just purchase a 2.5K ohm linear taper pot. Something small would be nice. Connect one of the pot's end terminals to NE5044 pin 8. The other end goes to pin 15. The center terminal (wiper) goes to Pin 5. Done!

For gear/flap switch use, I think I will steer you into a more flexible arrangement than usual. This takes more parts but is worth it.

(5) The attached schematic (next post) can use a two position on/off switch for left-right servo positions or an On/Center-Off/On three position switch for left-center-right servo positions.

Be VERY careful, or you will render your prized Tx into a high tech paper weight. Double check your work!

Let us know how it goes. Please post photos for all to see.

Best Regards,
Mr. RC-CAM
Last edited by Mr.RC-CAM; Aug 08, 2002 at 04:55 PM.
Aug 08, 2002, 04:54 PM
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Schematic....
Aug 08, 2002, 05:06 PM
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you rock
Sir!
Aug 08, 2002, 06:59 PM
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Checked my stock of resistors and found I don't have the correct ones, so I will have to purchase them.
I'll post my results when I'm finished.
Your assistance is very much appreciated BTW.
Thanks!
Aug 08, 2002, 10:20 PM
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When you get it running please post a full report. I hope to hear good things.

Regards,
Mr. RC-CAM
Aug 09, 2002, 07:45 AM
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Just a couple more questions:
Use 1/4 watt resistors?
Any chance to utilize one more channel on this TX?
Thanks


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