circuit fade

[4pyros]

Throbscottle and 4pyros,

I have connected 2 x 1uF polarised caps, as the circuit asks for a 1uF non-polarised, and I have read that this is a way of doing it???

Thats only to pass an audio signal!
You are making a power supply of sorts.

 

[camerart]

Thats only to pass an audio signal!
You are making a power supply of sorts.

4Pyros. Correct me if I'm wrong. Are you saying?:

"Thats (non-polarised caps) only to pass an audio signal!" Yes/no

"You are making a power supply of sorts." This circuit, is for making a power supply of sorts. Meaning, a louder sound input, gives a higher voltage, and the high/low voltage switches the relay. Yes/no

Are both these parts required for the application?

 

[camerart]

The relay is for switching a jackplug that can be removed from the radio. The jackplug simply shorts to make the connection.

Please bear this in mind, when advising on transistor/relay substitute.

 

[camerart]

Yes that is an acceptable way to make a non-polarised cap from twp polarised caps. However the circuit does not need a non-polarised cap! Just use a normal 1uF cap with it's - lead to ground.

You are only half wave rectifying the transformer signal, so you are getting all the power transferred as DC. This will be causing issues over time with the sound card output as it is capacitor coupled.

Replace the diode with a 4 diode "bridge rectifier" so that balanced AC is used from the soundcard->transformer->transistor base. Also you need a resistor across the transistor base (base to gnd), try about 470 ohms to 2.2k. That will give a more defined ON/OFF point and give better relay turnoff.

Hi Mr RB,

See attachment: I have also added an optoisolator, from other suggestions (The radio key, reads 12V 10mV) Is this what you are suggesting? does it look ok?

D1-4 1N4148

Cheers, Camerart.

 

[Mr RB]

Everything up to the transistor looks good. I would suggest you try that with the relay and check the "fading" problem is all fixed now, if that test ok then you could change to the opto coupler, which could ideally replace both the transistor and relay.

 

[camerart]

Everything up to the transistor looks good. I would suggest you try that with the relay and check the "fading" problem is all fixed now, if that test ok then you could change to the opto coupler, which could ideally replace both the transistor and relay.

Good. Do you think the rectifier will output enough to drive the opto isolator? If so then it looks as though it doesn't need the 12V and earth. Is this correct?

 

[Mr RB]

If it is the soundcard speaker or headphone outlet (not the line outlet) it has enough power to drive a 16 ohm headphone at maybe 100mW or more, so that would be enough to make a few mA through the LED in the optocoupler.

If you are eliminating the transformer and putting the bridge rect directly on the sound card speaker output use a 15 ohm resistor in series, and a resistor across the LED like 2k7. That is assuming you can tweak the soundcard output level via the PC so you don't kill the LED from being too loud. It might be wise to start with say a 1k resistor in series instead of the minimum 15 ohms, for LED safety, and then tweak the value of that resistor until you get good performance.

If you had a 'scope it gets easier as you could drive the soundcard output into a resistor and measure the voltage/current etc that it will provide.

 

[camerart]

If it is the soundcard speaker or headphone outlet (not the line outlet) it has enough power to drive a 16 ohm headphone at maybe 100mW or more, so that would be enough to make a few mA through the LED in the optocoupler.

If you are eliminating the transformer and putting the bridge rect directly on the sound card speaker output use a 15 ohm resistor in series, and a resistor across the LED like 2k7. That is assuming you can tweak the soundcard output level via the PC so you don't kill the LED from being too loud. It might be wise to start with say a 1k resistor in series instead of the minimum 15 ohms, for LED safety, and then tweak the value of that resistor until you get good performance.

If you had a 'scope it gets easier as you could drive the soundcard output into a resistor and measure the voltage/current etc that it will provide.

Thanks MR RB,

How I understand it: Put a 1k resistor (series) (adjustable) from the earphone socket. Test the output with a Scope (I have one) low/high volume, see what it puts out, fit a fixed resistor from results.

If the output is sufficient for the LED (1.3V ??), the transformer isn't needed. Add 2k7 across LED.

 

[camerart]

If it is the soundcard speaker or headphone outlet (not the line outlet) it has enough power to drive a 16 ohm headphone at maybe 100mW or more, so that would be enough to make a few mA through the LED in the optocoupler.

If you are eliminating the transformer and putting the bridge rect directly on the sound card speaker output use a 15 ohm resistor in series, and a resistor across the LED like 2k7. That is assuming you can tweak the soundcard output level via the PC so you don't kill the LED from being too loud. It might be wise to start with say a 1k resistor in series instead of the minimum 15 ohms, for LED safety, and then tweak the value of that resistor until you get good performance.

If you had a 'scope it gets easier as you could drive the soundcard output into a resistor and measure the voltage/current etc that it will provide.

I think I've got this correct???

Output from earphone, nothing else connected 40mV Peak to Peak.

Connected to the transformer, primary as before 40mV, secondary 3.5V Peak to peak.

Connected to the rectifier, output 1.2DC. I think the led needs 1.3vDC.

Connected a led through a 1k resistor and 12v to the opto output, led not lighting, no volts.

 

[Mr RB]

Are you measuring the 40mV using your multimeter on AC range? That is not an accurate reading, probably due to the meter being optimised to 50/60Hz measurement and the soundcard signal being hundreds of Hz.

If you don't have a scope it's abit harder to measure but you can still do a simple test. You are on the right track seeing if a LED light s up. Just try the bridge rectifier and LED with a small cap across the LED like 0.1uF. Use a smaller series resistor than 1k, try 100 ohms or 220 ohms. Then slowly turn up the sound card and the LED should light when the soundcard output voltage is greater than the rectifier drops (about 1v) plus the LED drop (about 1.3v).

If your soundcard only makes 1.2v after the rectifier you have probably connected to the line out plug, which only makes about 2v p/k when turned right up and is designed to drive powered speakers and amplifier inputs. You need to connect to the headphone plug (the LOUD output) which drives a headphone or small speaker directly.

 

[camerart]

Are you measuring the 40mV using your multimeter on AC range? That is not an accurate reading, probably due to the meter being optimised to 50/60Hz measurement and the soundcard signal being hundreds of Hz.

If you don't have a scope it's abit harder to measure but you can still do a simple test. You are on the right track seeing if a LED light s up. Just try the bridge rectifier and LED with a small cap across the LED like 0.1uF. Use a smaller series resistor than 1k, try 100 ohms or 220 ohms. Then slowly turn up the sound card and the LED should light when the soundcard output voltage is greater than the rectifier drops (about 1v) plus the LED drop (about 1.3v).

If your soundcard only makes 1.2v after the rectifier you have probably connected to the line out plug, which only makes about 2v p/k when turned right up and is designed to drive powered speakers and amplifier inputs. You need to connect to the headphone plug (the LOUD output) which drives a headphone or small speaker directly.

Where I have said peak to peak, this is a reading from an oscilloscope.

All taken from the earphone output.

Where I said the LED does not light up, this is at the opto coupler output..

 

[Mr RB]

40mV is not right for a headphone output! The line output should be 1-2v p/p and the headphone output up to a few volts, and a 16 ohm headphone set should pretty much blow your ears off if it is turned up fully. Do you have some headphones/earphones around?

If you are getting 40mV p/p on the scope from the headphone output, how many volts p/p do you get from the line output plug?

Also what is generating the audio signal to the soundcard and does that have a volume control? Maybe it is turned right down?

 

[4pyros]

40mV is not right for a headphone output! The line output should be 1-2v p/p and the headphone output up to a few volts, and a 16 ohm headphone set should pretty much blow your ears off if it is turned up fully. Do you have some headphones/earphones around?

It may need to be properly loaded to see the right voltage. Cheak it with the headphones attached if you can.

 

[camerart]

40mV is not right for a headphone output! The line output should be 1-2v p/p and the headphone output up to a few volts, and a 16 ohm headphone set should pretty much blow your ears off if it is turned up fully. Do you have some headphones/earphones around?

If you are getting 40mV p/p on the scope from the headphone output, how many volts p/p do you get from the line output plug?

Also what is generating the audio signal to the soundcard and does that have a volume control? Maybe it is turned right down?

I tried a new and an old set of earphones. One was quiet one was loud.

I verified the readings with a second oscilloscope. These are not calibrated, but checked with two different voltage batteries. The first oscilloscope (The one I have been using) has a setting 1=10mV/Div This appears to give 100mV/division ???? (I would have reported 60mV)

Anyway. Using earphones to load the earphone (No other output) I get 600mV with no earphone. 200mV Peak to Peak with earphone loading it.

When connected into the circuit, loaded by transformer. Primary 1V, secondary 3V, after rectifier, 1.2V.

I noticed that lowering the volume, doesn't seem to lower the voltage at the chip as much as I thought.

 

[unclejed613]

i'd like to ask a question here about the radio..... what is it? is it a radio that has SSB capability? if so you can eliminate the whole hassle of building a keyer, and feed the radio audio from the sound card. a single frequency tone (like what i assume you are feeding the keyer with) will act like a CW carrier on an SSB radio. this is how most CW is done these days. the transmit switch is held down and the audio tone creates the carrier. so if the radio is tuned to 14.000 MHZ USB and your tone is 1khz, the CW is transmitted on 14.001Mhz.

 

[camerart]

i'd like to ask a question here about the radio..... what is it? is it a radio that has SSB capability? if so you can eliminate the whole hassle of building a keyer, and feed the radio audio from the sound card. a single frequency tone (like what i assume you are feeding the keyer with) will act like a CW carrier on an SSB radio. this is how most CW is done these days. the transmit switch is held down and the audio tone creates the carrier. so if the radio is tuned to 14.000 MHZ USB and your tone is 1khz, the CW is transmitted on 14.001Mhz.

I've just built a FOXX-3 transceiver. I'm learning Morse, and I'm sure it will be a while before I can type a sensible speed. This is why I'm building this project. Once I get some results, I will know which radio to buy.

What you say is interesting. I am building a circuit, that interfaces between a computer and a radio. I type the Morse into the computer and the interface keys the Morse, into the radio. Is this the same as what you are explaining?

 

[4pyros]

When connected into the circuit, loaded by transformer. Primary 1V, secondary 3V, after rectifier, 1.2V.

That should be able to light an LED. Have you tryed it with a low value current limting resister?

 

[MikeMl]

I'm late to the party, but my concern is that the original circuit, and most of the follow on is missing one critical component: there is nothing to limit the current when the sound-card output swings positive. There needs to be a ~1k resistor between the cathode of the diode, and the base of Q1.
As published, the circuit is greatly overloading the audio amp inside the sound card, likely causing it to overheat, and "fade".

I recognize the original circuit as coming from an ARRL publication (likely QST). They publish some awful circuits created by novices (not a class or radio license ). You would think they would have some technical editors that could review contributed circuits.

 

[camerart]

Ok, Thanks all, for your replies.

I am now on the MrRBs circuit, he also suggested a 1K resistor, in series with the LED and a 2K7 across it. See #24. Hoping for the transformer/rectifier to supply enough for the LED, without the transistor.

It looks simple but I seem to be spending hours on it. I attached an external led so I could see it instead of the opto isolator, it didn't light with or without a resistor. I then tried the led on a 1.5V battery, and it didn't light. Then a 3V and it lit. (I test them with a very quick touch, then add a resistor to suit)

Regarding the circuit, it seems that the rectifier part takes all of the energy out of the system.

 

[MikeMl]

...

Regarding the circuit, it seems that the rectifier part takes all of the energy out of the system.

Attached is how the two circuits should look with the current-limiting resistor. This is to solve the sound-card overload issue.

What is the turns ratio of the transformer you are using. Line-Out of a sound card is usually about 1Vpp. If the transformer is 1:1, the 1V is not enough to forward-bias both the diode and the transistor base or the LED. You would need a transformer that has a turns ratio higher than 5:1 (hooked up backwards, so that it steps up the line-out voltage). An old output transformer from a "transistorized radio" 500Ω to 8Ω hooked up backwards would an ideal step-up. That would give you about 10Vpp to drive the rectifier and follow-on circuit...