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   Home   Help Search  
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Author Topic: Icom 718  (Read 10538 times)
NA4IT
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« Reply #15 on: August 20, 2016, 06:30:33 AM »

Or you could just buy a Signalink USB....
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VU3DES
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Posts: 10




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« Reply #16 on: August 20, 2016, 11:13:02 PM »

Or you could just buy a Signalink USB....

@NA4IT Homebrewing is what I love most about this hobby.  I spend more time making this stuff than really using it on air.  VOX serves my purpose, CAT will not hamper my activities on air.  But it's just fun to learn and make it yourself you know..

Getting back to my issue.  If any Amateur has a suggestion I'd appreciate your help !
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W9IQ
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« Reply #17 on: August 21, 2016, 04:22:05 AM »

You have inadvertently inverted the logic of the CI-V signals by the way you have wired IC2 and IC3.

For example, when the CI-V signal is high, the LED in IC1 is biased on. This turns on the transistor in IC1 which then pulls the RxD pin on the USB dongle low. This results in high input, low output.

Similarly when the USB Tx pin is high, the LED in IC3 is biased on. This turns on the output transistor which pulls the CI-V signal low. This results in high input, low output.

You can see that you do not want this inversion since the cable works fine when directly connected. I hope that helps.

- Glenn W9IQ



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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
NA4IT
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« Reply #18 on: August 21, 2016, 04:36:17 AM »

I agree homebrewing MUST be a part of this hobby. But after building MANY interfaces, and spending a good $300, once I bought the Signalink USB and a CAT cable, all the RF problems and incompatibility went away. And, I had a clean signal on the air. I see so many digital signals splattering everywhere coming from homebuilt interfaces. I know a lot of it has to do with settings also.
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W9IQ
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« Reply #19 on: August 21, 2016, 04:46:35 AM »

Sometimes it is not the cost of the parts, but the value of learning and the pride of accomplishment.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
VU3DES
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« Reply #20 on: August 21, 2016, 09:23:02 PM »

You have inadvertently inverted the logic of the CI-V signals by the way you have wired IC2 and IC3.

For example, when the CI-V signal is high, the LED in IC1 is biased on. This turns on the transistor in IC1 which then pulls the RxD pin on the USB dongle low. This results in high input, low output.

Similarly when the USB Tx pin is high, the LED in IC3 is biased on. This turns on the output transistor which pulls the CI-V signal low. This results in high input, low output.

You can see that you do not want this inversion since the cable works fine when directly connected. I hope that helps.

- Glenn W9IQ

Thanks Glenn,  I see the silly mistake I am doing Cheesy

Just to re iterate, If I add a Transistor switch (like i did with the PTT line) in both TXD and RXD lines, that should fix my issue right??  

Or may be I just use a fast enough Opto coupler which doesnt invert the output.  Could you advise on those lines too ??

Or could adding a Pull down resistor from emitter to ground on 4N25 help ??
« Last Edit: August 21, 2016, 11:50:12 PM by VU3DES » Logged
W9IQ
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« Reply #21 on: August 22, 2016, 06:21:59 AM »

Amogh,

You can use your transistor technique to correct the logic through IC3, the same way you did for IC1.

To correct the logic of IC2, it is actually a little simpler, but allow me to explain why in order to help your understanding of how the CI-V control circuit works.

The CI-V transmit (output) circuit inside the IC-718 is essentially an open collector transistor. This means the emitter is grounded and the collector is attached to pin 1 of J1 in your circuit (I say "essentially" since there is actually a resistance of about 40k tied high to 5 volts inside of the transceiver but this is to bias the receive side of the CI-V circuit inside the 718). As a result, the transistor and CI-V circuit cannot source any current, it can only sink current. Your present circuit assumes that the CI-V connection is capable of sourcing current for the LED in IC2 but this will never work.

To take advantage of this open collector and to correct your inverted logic of IC2, make the following changes:

  1.) Connect pin 2 (LED anode) of IC2 that was connected to ground, to pin 1 of J1 (CI-V).
  2.) Connect the side of R5 (470) that was connected to pin 1 of J1, to pin1 of P3 (VCC).
  3.) R6 (4.7k) could then be eliminated but this is not strictly necessary.

Now when the transceiver turns on its open collector transistor, current will flow through the LED in IC2. This turns on the transistor in IC2. So now low in equals low out.

Note: I assume that your voltage on pin 1 of P3 is 5 volts. If that is not the case, you will need to change the value of R5 to properly bias the LED.

I hope that helps. Let me know if you need clarification on any of this.

- Glenn W9IQ



« Last Edit: August 22, 2016, 08:54:35 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
VU3DES
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Posts: 10




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« Reply #22 on: August 23, 2016, 12:09:50 PM »

Hi Glenn,

Thanks for the explanation.  I read about the Open collector part of the CI-v output and now understand the sinking current part in the CI-v side.


  1.) Connect pin 2 (LED anode) of IC2 that was connected to ground, to pin 1 of J1 (CI-V).
 

Here, did you mean Pin 2 LED cathode  of IC2 ??

Anyways, I made the following changes and it still doesn't work.  I have a doubt.



When pin 1 on J1 is low, led in IC2 glows and transistor is biased pulling output low.
and when j1 is high, both anode and cathode of led in IC2 are high, transistor not biased and output remains high.  (this is as it should be) so fixed.

Now on IC3 when computer side input pin1 is high, led glows and transistor biases making output j1 low.
and when pin 1 of IC3 is low, IC is unbiased and output remains high.

we have now solved the RXD line inverting.  how can this also apply to IC3, i.e. the txd line ??


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W9IQ
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« Reply #23 on: August 23, 2016, 12:27:54 PM »

Amogh,

You are correct, I should have said cathode of IC2, pin 2 connected to J1 pin 1. You have it drawn correctly.

In my last post I said:

Quote
You can use your transistor technique to correct the logic through IC3, the same way you did for IC1.

By this I meant you should add a BC 547 transistor to IC3 with its 1k base resistor in the exact same way you did for IC1. The transistor emitter goes to pin 2 of IC3 and the transistor collector goes to pin 1 of IC3. The free end of the base resistor goes to Pin 2 (TxD) of P1. The 470 ohm resistor that was connected to Pin 2 (TxD) of P1 now goes to Pin 4 (VCC) of P1. This will correct the logic for that circuit.

Hopefully you will then have a working circuit. Diagnostic LEDs could be added if needed but let's see what this next step does for you.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
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