[time-nuts] TASS Computer-Controlled Switch System

Wed Sep 30 13:17:55 UTC 2015

Thanks, Tom.  These sorts of projects are why I disappear from the list 
every now and then -- what started out as an afternoon tearing apart one 
of the HP switches turned into a major design project, and the other 
stuff fell by the wayside.

The Arduino platform ended up being a great choice.  There are so many 
widgets available (along with support libraries) that adding bells and 
whistles is easy.  I'd never done a line of graphics coding in my life, 
but I was able to write the touchscreen interface in a weekend.  Adding 
ethernet connectivity took an afternoon, and I expect WiFi won't take 
any longer.

I'm also glad I made the decision to put absolutely zero intelligence on 
the switch board itself.  One of the SDR radios widely used in the ham 
community provides 7 open collector control signals that can be set 
based on frequency band.  It turns out that a pair of 3 bit decoder 
chips are all that's needed to let that radio fully control the switch, 
with no Arduino required.

I haven't tested the dynamic switch performance as you suggested. 
However, the relay set time is <3ms so in most cases there should be 
ample time for things to settle down.

The relays have a rated 5e7 mechanical operation lifetime, and 1e5 
switch-at-full load (~30W) operations.  They've a very standard 
form-factor and are available from at least a couple of sources.

(And by the way, early on there was lots of discussion about solid-state 
switches, etc., but to meet the requirement of handling DC-150MHz with 
no clipping or distortion issues, mechanical relays were the only choice.)

John
----

On 9/30/2015 1:23 AM, Tom Van Baak wrote:
> John,
>
> Thanks for making this available. I can only imagine the amount of work that went into it. Having used many of the same HP RF GPIB switches as you over the years to do multi-device routing and timing, the TASS geometry is very clever; several steps above what HP did. The decision to use the Arduino shield form-factor is spot on. I suppose we are all now imagining multiple layers of Time & Frequency shields.
>
> The first person to put a sub-ns PICTIC II on a shield gets a special prize.
>
> A year ago I thought this was just a T&F project but I see you neatly evolved it to a generic ham tool as well. Hopefully that community will help make this a success.
>
> One question -- because of cable or load changes do you see any noise or disturbance on the first or second reading after you change the switches? Also, what's the rated lifetime of the switches?
>
> Thanks,
> /tvb
>
>
> ----- Original Message -----
> From: "John Ackermann N8UR" <jra at febo.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>; <volt-nuts at febo.com>
> Sent: Sunday, September 27, 2015 7:19 AM
> Subject: [time-nuts] TASS Computer-Controlled Switch System
>
>
>> Every so often, I hijack the list to do some shameless self-promotion
>> when I think it would be of interest to the 'nuts community.
>>
>> I've spent the last several months developing a computer-controlled
>> relay switch system.  The impetus was failure of the old HP 59307A GPIB
>> switches in my PPS measurement system and discovery that replacement
>> relays are unobtainium.  The only similar remote switches I could find
>> cost >$1K, which seemed a bit rich.  So, I decided to roll my own.
>>
>> We ended up with an 8 port switch board controlled by an Arduino.  I
>> think it will have lots of T&F applications as well as usefulness in ham
>> shacks.  Like virtually everything I do, it ended up as a TAPR kit.
>>
>> There's an introductory video at https://youtu.be/P-TUM2dOi4c
>>
>> The relay board kit is $119 and we have a shield for the Arduino Mega
>> 2560 that can control 4 relay boards and costs $19.  The software is
>> open source.The boards are now available from TAPR at
>> http://tapr.org/kits_tass.html
>>
>> (BTW, I contribute my designs to TAPR and don't have any financial
>> interest in sales.)
>>
>> Special thanks to time-nuts Bob Camp and Tom Holmes for a lot of
>> engineering assistance.
>>
>> Here's the TAPR product announcement:
>>
>> "
>> Now Available: The TASS Computer-Controlled Switch System
>>
>> The TASS (Totally Awesome Switch System) is a general purpose 8 port
>> DC-150 MHz relay-based switch. The hardware is designed to be very
>> generic, with an inexpensive processor such as an Arduino providing the
>> system logic. Control is via USB, with ethernet and other interfaces
>> also available.
>>
>> The TASS can be configured several ways, and multiple boards can be
>> combined to create large switching systems. The TASS has many uses, from
>> switching signal sources on a test bench or in a laboratory, to
>> selecting receive antennas and filters in a ham or SWL station.
>>
>> The TASS system has two boards:
>>
>> *  The TASS-R relay board, which does the mechanics of signal switching
>> and provides a very simple 10-pin interface.
>>
>> *  The TASS-SHIELD board for use with an Arduino Mega 2560
>> microcontroller. The TASS-SHIELD allows up to four TASS-R boards to be
>> controlled simultaneously.
>>
>> Both boards are available now from TAPR as kits.  They use through-hole
>> parts and don't require any special assembly techniques.
>>
>> The final component is open source software for the Arduino that acts as
>> an interface between a host computer or other input system, and the
>> switching hardware.  The software is available for download from TAPR.
>>
>>
>> An introductory video is available at
>> https://youtu.be/P-TUM2dOi4c
>> or from TAPR at
>> http://tapr.org/~n8ur/TASS/TASS_Intro_26Sep15.mp4
>>
>> Software and documentation can be downloaded from
>> http://tapr.org/~n8ur/TASS.
>>
>> You may order the TASS-R and TASS-SHIELD boards by visiting
>> http://tapr.org/kits_tass.html
>> "
>>
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