[time-nuts] TASS Computer-Controlled Switch System

Wed Sep 30 09:23:47 EDT 2015

Oh, and also to your question about load changes:

a) the RF connections on the board are all 50 ohm stripline and have a 
pretty good match.  At VHF frequencies, the topology results in a 
transmission line stub effect which does limit the high end of the 
frequency range.  The PCB is 4 layers to allow for true stripline layout.

(b) there are 50 ohm termination resistors on all the non-selected 
inputs, so you're not switching from an open circuit condition.

John
----

On 9/30/2015 9:17 AM, John Ackermann N8UR wrote:
> 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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