[amsat-bb] Falconsat Success

Scott scott23192 at gmail.com
Sun Oct 22 19:38:42 UTC 2017

Glad to help, Tony.  I'll reply to the mailing list in case anyone else is 

First, your computer needs a port (usually serial) to trigger the relay.  My 
computer did not have one, so I bought a USB > Serial cable.

There are discussions online regarding that the different types of USB > 
Serial cables do or don't work for this purpose.  The following cable is 
working well for me:


(if you don't already have a charity linked to Amazon's "SMILE" program, now 
is a good opportunity to set that to AMSAT!)

As I mentioned earlier, to make it easier to access the serial pins you 
need, a breakout adapter is handy.  Others may wish to solder a permanent 
connection, but I use the following:


... and to save people having to scroll through previous posts, here is the 
relay itself:

https://smile.amazon.com/gp/product/B00E0NTPP4   (please note that we'll 
only be using one of the two relays on that board)

And now to actually answer your question, I threw together an ugly image 
file that shows the physical wiring connections as well as the schematic so 
you can know what it's doing.  I also included a screen print of where I 
have the PTT Com port selected in HS_Soundmodem.  Of course the Com Port 
number will be different on everyone's computer and on top of that, you 
might be using something other than HS_Soundmodem to control your PTT from 
the computer.  But in the following diagram, you can see how I'm setup for 


... hope that helps!

You also asked about drivers, etc., on a Windows machine.  Other than 
allowing the USB > Serial cable to install whatever it needs to download to 
function, you'll be fine.  The computer has no idea that the RTS signal on 
your serial port is controlling a relay.  So, nothing is needed on the 
computer for the relay itself.

And as for the 5 VDC to power the relay coil, you could certainly use an AC 
adapter of some kind, but I just cut the end off of a short USB printer 
cable and used the red & black wires to give me a convenient 5 VDC from the 
computer (or in my case actually from a multi-port, powered USB hub).

-Scott,  K4KDR


-----Original Message----- 
From: Tony
Sent: Sunday, October 22, 2017 2:11 PM
To: Scott
Subject: Re: [amsat-bb] Falconsat Success


That's exactly what I'm looking for. The fact that it has isolation is a
real plus. Could you pass along a few more details regarding the type of
USB cable used and how you wired the relay to your PTT line on the rig?

I'm not much of a PC guy so every bit helps - never home-brewed a USB PTT.

Thanks Scott

Tony -K2MO

On 10/22/2017 9:39 AM, Scott wrote:
> Congrats, Tony!
> The following relay has been working very well for me to handle PTT:
> https://www.amazon.com/gp/product/B00E0NTPP4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
> ... I use 5 VDC from a USB cable for the coil voltage with the application
> of that coil voltage being triggered by the serial RTS signal from
> HS_Soundmodem.  The above relay is great for that since the coil circuit 
> is
> controlled by an opto-isolator that can be operated by a low level signal
> like the serial RTS.
> The following item sure made it easy to attach a pair of wires to serial
> RTS & ground:
> https://www.amazon.com/gp/product/B00WW6P636/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
> -Scott,  K4KDR
> ===================================
> On Sun, Oct 22, 2017 at 4:39 AM, Tony <dxdx at optonline.net> wrote:
>> All:
>> Managed to work Falconsat this morning using UZ7HO's Soundmodem, WISP and
>> VSP. I don't have a PTT circuit so I had to use the rigs MOX function to
>> send file requests. I wouldn't recommend doing that for obvious 
>> reasons --
>> need to build a PTT circuit ASAP.
>> If anyone is interested, this video guide shows the basics on how to 
>> setup
>> Wisp and Soundmodem using HW-VSP.  See: https://www.youtube.com/watch?
>> v=1ahlA-bRb5A
>> 73, Tony -K2MO 

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