© Lorem ipsum dolor 2010 Tony - LU7DTS -  Campana - Argentina   My friend Ermes, IK4OLY from Carpi (MO) Italy has made me know a circuit that he developed  based on an earlier project aimed to control an UHF repeater. I thank Ermes to allow me to  publish his electrical circuit  and  picture of the project. While the original circuit operates at 12  volts, Ermes modified some component values in order to be powered with 5-volt aiming to use  with  portable PC (notebook or netbook) from their  USB port can be  obtain +5-volt to power the  interface  Circuit details  The project includes a vox control, just to avoid using serial port. A very common  integrated  circuit like a LM358 dual op amp and the Optocoupler 4N32 were used. Many amateurs prefer a  total isolation between the PC ground and the transceiver VHF / UHF ground . So you will see  that the printed circuit board ground will be connected only to PC's ground, that ground will be  completely isolated from the TRX ground mass.  To achieved this objective two audio transformers (600 ohms 1:1 ) which maintain isolated. the   ground  masses.  These transformers similar to those used in earlier version of telephone  modems.  The resistor  R9 value should be between 330 ohms to 1.2 Kohm;  a larger value reduces the  brightness of the LED and therefore the power consumption during VOX activation.    The VOX time delay is controlled by the transistor Q1 (BC337), which loads the electrolytic  capacitor C2 through variable resistor VR4. The delay will result  between 0.2 and 2.5 seconds.  To increase this delay time you can change the variable resistor VR4 from 500 Kohm up to 1M   and  selecting  C2  with a capacity of 10 µF.  These changes should  allows you to control the  VOX time delay between 0.4 and 5 seconds.        In order to facilitate the  construction of this interface I  designed a circuit board using   PCBWizard software.  Fig 2 to  the left shows components  mounted on PBC .   On upper part of PCB find the  VOX control circuit. Below is the  audio circuit using two audio  transformers in order to  isolate  the PC and TRX grounds  The 4N32  is an Optocoupler with  Photodarlington Output transistor.  In case you have in stock a  Photoisolator like 4N26 with transistor output  I designed the PCB taking into account both  possibilities: the 4N32, which includes  a Photodarlington output  and 4N26 type that has only a  single NPN transistor as output. On the left find the figure where you can see the circuit using a  4N26, in this case a NPN transistor  BC337 should be added.  To the left figure shows how to wire  the PCB when using Optoisolator  4N26  wich includes Q2, BC337.  To the right you can see how to wire  the PCB when  using a 4N32  Optocoupler. In this case, instead of  using  an additional BC337 (Q2)  transistor, a flying wire must be  place between the base and emitter   pads as shown.   If the transceiver PTT requires  less than 100 mA,  you can use the 4N26 Optoisolator  alone,  without BC337 (Q2) and put the flying wire as it was explained in 4N32 PCB wiring.  Fig 3 shows the mirror image of copper side of this printed circuit board (PCB).     By clicking on the Fig 3 image  you can  download a PDF file containing this design.  Please use this PDF file without reducing or  enlarging  when printing. It must be printed  actual size (100%).   IK4OLY Protopype Fig 4 shows the project prototype  made  by Ermes, IK4OLY on a single side  perforated board. As mentioned before  this prototype was made to be used with   laptops, notebooks, or  netbooks  that  have no serial port. The  interface is   powered from USB port (+5 V)  Fig 5 shows the same  interface project done  on a printed circuit  board (PCB). PCB was design using  PCBWizard program.  Nella Fig 6 si può vedere il circuito stampato  (PCB) lato rame. La Fig.7 invece mostra il  “layout” dei componenti sul circuito stampato.  .   Fig 8 shows the preset calibration of control circuit VOX: VR3 controls audio input level, VR2  controls VOX gain, VR4 controls VOX delay ("tail"), between 0.2 and 2.5 seconds.   Eventually you can manage to increase the VOX delay time by changing VR4 value up to 1 M  ohm and C2 up to 10 uF as explained before.   EchoLink will continue sending audio to the station on the Internet for a short amount of time after  the signal stops.   Consumption:  This current in standby is  less than 1 mA while during activated VOX  the current should rise up to  approximately 10 mA.  As you can see this interface is very suitable for portable PC do to its very  low consumption.   Additional information:  Those of you who wish to modify the design of this interface can download a compressed zip file,  where you will find the PCBWizard file for PCB design  as well as the LiveWire file for electrical  circuit design.   To download this compressed file  click here   In case you prefer not to use the PCB boar along with all connection  cables permanently attached  to it, is possible housing this project in a suitable box. The alternative is to use a box with panel  chassis connectors to avoid connection cables to be attached permanently to the box.   Obviously this is not the only possibility left to the reader  investigate other valid alternatives.   For my project I made the box using PVC free foam sheets  which are easy to handle,  cut and drill using conventional  tools.  Also very easy to glue with cyanoacrylate glue or similar  type.   I put a 4 pin mini-USB (type B) chassis connector in order to  use a standard USB to mini-USB cable (Type A to Type B)  to  get the +5 V form. Fig 9 shows details of USB connectors A  and B.  .   Fig 10 shows the front side of the  box where I put a potentiometer  (VR4) to control the VOX delay, D1  yellow LED to indicate when VOX is  activated and an additional red LED  (with a 1.2K resistor in series) to  monitor the +5 V.   Fig 11 shows the back side of the container box where I put the mini USB type B connector and  two 5-pins male panel chassis connectors, one for the TRX and the other one for the PC.   Fig 12 shows the top view.  EchoLink Sysop Setup If you are going to use a EchoLink Sysop Fig 14 shows  how to Setup the TX Ctrl .  You must activate “External VOX”   Acknowledgment I wish to thank Ermes, IK4OLY in giving me the opportunity to publish his project on this site, as  well as the spelling of the page in Italian language.  Final Words:  This interface is very simple to make and setting up. Very versatile for digital modes and for those  who want to install an EchoLink Sysop.   I encourage you to make this project and I wish you an excellent construction.  Tony - LU7DTS   Fig 2 Printed Circuit Board Components side.  Fig 3 Mirror image of copper side  Fig 4  IK4OLY Interface prototype  Fig 5 PCB finished: Component’s side   Fig 6 PCB finished: Copper side.  Fig 8 VOX circuit setting   Fig 7  Components layout  Fig 9  USB connectors A and B  Fig 11 Back side of the box  Fig 12 Upper side of the opened box  Fig 13  Finished VOX Interface  Background Fig 14 - EchoLink Sysop Setup  Fig 1  Electrical circuit of this VOX interface