Tuesday, 19 October 2010

A mind boggling USBlink VOX data interface

After Julian G4ILO published the story and diagram of his very nice USBlink data interface I thought it was easy to make one myself. There are only 3 active components, the USB soundcard is already made and the diagram was not that difficult. Since I am a technician (not a electronics engineer) I thought I could not mess up. I had my own idea about it, thinking about a USB stick like interface which saves me a cable and is easier when in the field or on vacation with a portable set. Anyway, I set it up and made shure everything was connected like it should. In my opinion to test it is not necessary to connect the radio, the red LED should blink as soon as the audio is playing. But it isn't... Since I noticed the USB stick was warming up I suspect the LED, and yes I connected it the wrong way. Just to be shure I tested it with a 5V supply and the LED was blinking. Now when connected the right way, the USB stick stays cool, the green LED is blinking as soon as I inject PSK31 from FLDIGI like it should, but the red TX LED still isn't blinking. I do know some simple basics of electronics but I am certainly not a engineer. From my job I know to solve a problem just to go through some logic steps. So this is what I did:

- I tested the USB soundcard, max. output. Green LED is blinking when transmitting PSK31. I can measure
1,5V AC at the output. Just to be shure I tested another one too, same results.
- I measured if I had +5V DC on the TX LED, yes I did
- I measured both switching transistors for PTT and TX LED but neither does switch to the ground when PSK31 is injected in the VOX.
- I  removed the TX LED and the switching transistor just to get to the basic VOX diagram, but still the PTT switching transistor does nothing.
- Of course I tested all components before use as they are from used printboards. As far as I know they are all working. Though I'm not shure how to test the transistors, if I measure them with a ohm meter they all give the same results.
- I checked all solderings and connections, all are solid and ok!

Still the VOX is not working, did I overlook something? I need some help, some advice will be very welcome as I would really get this (simple) USBlink VOX interface to work.

Nadat Julian G4ILO zijn verhaal gepubliceerd had over zijn USBlink interface dacht ik dat ik zoiets makkelijk zelf zou kunnen maken. Met maar 3 aktieve componenten en een vrij eenvoudig schema zou het mij als monteur (geen electronica ing.) niet kunnen mislukken dacht ik. Ik had mijn eigen idee erover, namelijk een soort USB stick te maken zodat het me een kabel zou schelen, handig als je het op vakantie of mobiel wilt gebruiken. Dus alles maar in elkaar gesoldeerd en een paar keer gecontroleerd. Volgens mij is het niet nodig om een radio aan te sluiten om het ding te testen, dus FLDIGI opgestart en PSK31 aangezet. Helaas het enige dat gebeurde was het heet worden van de USB stick. Het bleek dat ik TX LED verkeerd om gesoldeerd had. Gauw de LED even getest op een 5V voeding en andersom op de print gemonteerd. Maar ook al blijft te stick nu koel, ik zie geen TX LED branden als ik PSK31 laat klinken... Nou weet ik als monteur (met alleen kennis van wat basis electronica) dat je storingen snel oplost door logisch na te denken en te beginnen bij het begin. Dit is wat ik heb gedaan:

- De USB stick getest, vol audio volume De groene LED gaat knipperen als ik PSK31 aanzet. Ik kan 1,5V wisselspanning meten op de uitgang. Voor de zekerheid een andere stick getest met zelfde resultaat.
- Ik meet +5V op 1 kant van de LED waar ik deze ook moet meten.
- Ik heb zowel de schakeltransistor voor de LED als PTT gemeten met audio in de VOX, maar deze schakelen niet naar de massa.
- Ik heb de TX LED + schakeltransistor verwijderd om zo het basisschema te krijgen. Maar ook dan schakelt de PTT schakeltransistor niet.
- Voordat ik begon heb ik alle componenten getest op een defekt omdat het allemaal sloopcomponenten zijn, alles leek goed. De transistoren heb ik met een ohm meter gemeten en geven allemaal dezelfde waardes. Het kan natuurlijk zijn dat ze alle drie stuk zijn, maar dat zou dan wel toeval zijn.
- Ik heb nogmaals alle verbindingen getest en alles zit precies zoals het moet.

Helaas doet de VOX het nog steeds niet. Ik kan dus wel een beetje hulp gebruiken. Ik hoop dat er iemand is die mij wat advies kan geven want het lijkt me toch leuk deze interface werkend te krijgen.


  1. It seems to me you didn't measure the voltage on the switching transistor. I saw about 0.6V when a signal is present, which is produced by rectification of the diodes. If not you need to trace the audio through that first transistor. If you used electrolytic capacitors make sure they are the right way round or you could be losing the switching voltage through leakage. You could also check the transistor is switching by applying a voltage to the base by say a 10K from the +5V rail.

    It's a learning process building stuff, though mostly what I learn is that no matter how hard I try I still put things in the wrong way round!

  2. Hello Julian, I didn't want to e-mail you personally as I know what your opinion is about problems with software etc. you made and described. But I appreciate your comment and advice very much. Besides that it might be interesting for others who want to build the USBlink interface.
    Well the capacitors are connected with the right polarization. I measure 0,75 V AC with PSK31 audio on the base of the first transistor. I measure 0,42V DC on the base of both switching transistors were you measure 0,6V. I tested both switching transistors applying DC through a 10K resistor to the base and they are switching ok (LED blinking). So I thought I just replace the first transistor, this time for a 2N2222 which I know is 100 percent ok. Then I noticed that the capacitor in the original design of Skip is 10 microF, I changed that too. But still I got 0,42V DC to the switching transistors. I think that my soundcard USB stick doesn't have enough audio output to trigger the circuit. I think I'll try a variable 4K7 resistor and see when the transistors are switching...
    More on that later. 73, Bas

  3. Update: Just don not get enough voltage on the bases of the switching transistors. I measured just before the 4K7 R but there the voltage is just 0,44V DC. Just before the diode that is connected in series between the cap and this resistor I measure 0,6V DC but exchange of this diode doesn't make it better. my knowledge of electronics is not good enough to change one of the components to get a higher voltage on the switching transistors.... 73, Bas

  4. Update 24-Oct: After exchanging almost all components and help from Julian I still cannot get this USBlink modem to work. In my opinion my USB soundcard doesn't have enough output to trigger the VOX, although I got volume control at 100%. In the mean time I found another VOX diagram which works with only 1 transistor. I probabely going to try to build it in the future. But for now I've had it with homemade electronics ;-(
    73, Bas


Thanks for your comment. Bedankt voor je reactie. 73, Bas