OBTAIN + and - 24V DC pulsing for old digital clock. HOW?

[Houseman]

Hi folks.
I have received week ago in my hands one of these old wall-mounted clocks that in the 70-80 were ticking time in Italian offices and public places.
You can find one of these searching on the web "SOLARI ICON 30"
After investigating a little bit on the web I found that the whole system was composed of a big Master Unit that had the clock circuitry inside plus the circuit to drive the Slaves Display Units (the one in my hand) connected all together via a 2-wire +/- 24DC channel.
Every new minute tick the master unit was sending on the bus a short +24V followed by a short -24V dc pulse.
Now the fact. Obviously one can assemble an horrendous and retro hardware relay circuitry that inverses the polarity of a 24V DC PSU...but I was thinking about a smoother circuit maybe an H-bridge circuit driven by an Arduino for example.
And here it where I stopped. Here is where my knowledge sinks. Can someone help me to design a circuit in order to send a +/- 24VDC pulse?
I was thinking about a square wave 48Vpp biased at -24VDC but is there a more nice and simple circuit that can do the job?
Any hint or even link to a data sheet is well accepted
Regards and respect to all, folks.
Steve

[Twoflower]

How about a H-Bridge?

[BrianHG]

If you want to use only a 24v supply, use 2 H bridges.  Flip your polarity back and forth, swapping one high & the other low, then switch both to 0 or off for 0v between the 2 output terminals.

You can also use 2 single, or 1 dual 24v capable mosfet gate drivers in this case.  They'll give you over an amp of current, some with as much as 5 for short instances, they usually come in a DIP8 or DIP14 package and all you need to give them is GND & 24v, plus feed the 2 digital inputs with your MCU.


Something like this:
https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/IXDN604PI/CLA335-ND/2352742

[Houseman]

Hi sorry for the delay, but I was abroad for work and never had the time to read post.
Thanks for the astonishing tutorial, evb149, much respect.
I am going to built the circuit and study the results.
The clock does not need any particular high current, not measured it yet but I assume a couple of mA should be enough. Even the duty cycle of the switching is not an issue, since the time interval is every minute
I am only afraid about the switching phase.
Will let you know but for now thanks again You and the other that answered my question.
Ciao!!

[Zero999]

Yes, an h-bridge IC will do.

L939 - cheap but relatively high voltage loss, although that might not matter and can be overcome by using a higher voltage power supply, if practical.
www.ti.com/lit/ds/symlink/l293.pdf

TLE5206-2 - more expensive and possibly overkill, MOSFET output, with a low voltage loss.
http://www.farnell.com/datasheets/1932119.pdf

[flynwill]

If you don't want to build something, there are several devices available that will drive your clock, this being a popular one:

http://www.kensclockclinic.com/products/1900w-unvr/

[ajb]

The proper retro solution would probably be to use a mains->24V transformer, with the mains frequency providing the timekeeping.  Depending on the pulse shape/timing requirements you may not even need to smooth the output of the transformer, but simply send a single full cycle of 24VAC to the clock for each minute tick.  Or maybe send a positive half-cycle and then a bit later a negative half-cycle. 

[Houseman]

Have tried it already.
Nothing happens. it simply needs pure -24V and the +24V 500ms pulse.
No 24VAC works.
Thanks

[Houseman]

If you don't want to build something, there are several devices available that will drive your clock, this being a popular one:

http://www.kensclockclinic.com/products/1900w-unvr/

Big thumbs UP!! Thank You
But a little bit too expensive.. 125 USD incl. shipping to Italy.
Want to try something less bucky.
I think with Arduino and some NTP have the same result for less than 50USD
But thanks again for sharing this to me.

[Chris56000]

Hi!

How about this:-

http://www.elektronika.ba/862/master-clock-driver-for-antique-slave-clocks/

Source-code, full schematics & hex for the PIC16F84 available from the article!

Chris Williams

[Houseman]

Thanks Pal. That's what I was searching for.
BIG THUMBS UP!!!!
 

[notfaded1]

Thanks so much for your post.  I have a clock in trying to drive
 .
https://photos.app.goo.gl/uXYj3mYeVZ1H3DP56
https://photos.app.goo.gl/jkeiYpx7TqrcX6yX6
https://photos.app.goo.gl/UtK5zZrVXXD1QaGu5

Bill