OBTAIN + and - 24V DC pulsing for old digital clock. HOW? - Page 1
Forum section: electronics / projects

author: Houseman
author_rank: Regular Contributor
timestamp: April 08, 2017, 03:59:31 pm
content: 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 acceptedRegards and respect to all, folks.Steve

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 08, 2017, 05:33:52 pm
content: How about a H-Bridge?

author: BrianHG
author_rank: Super Contributor
timestamp: April 08, 2017, 08:02:20 pm
content: 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

author: Houseman
author_rank: Regular Contributor
timestamp: May 01, 2017, 08:25:27 am
content: 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 minuteI 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!!

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2017, 09:37:46 am
content: 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.pdfTLE5206-2 - more expensive and possibly overkill, MOSFET output, with a low voltage loss.http://www.farnell.com/datasheets/1932119.pdf

author: flynwill
author_rank: Regular Contributor
timestamp: May 01, 2017, 01:46:09 pm
content: 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/

author: ajb
author_rank: Super Contributor
timestamp: May 01, 2017, 02:28:58 pm
content: 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.

author: Houseman
author_rank: Regular Contributor
timestamp: May 09, 2017, 11:43:23 pm
content: Have tried it already.Nothing happens. it simply needs pure -24V and the +24V 500ms pulse.No 24VAC works.Thanks

author: Houseman
author_rank: Regular Contributor
timestamp: May 09, 2017, 11:48:22 pm
content: Quote from: flynwill on May 01, 2017, 01:46:09 pmBig thumbs UP!! Thank YouBut 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 50USDBut thanks again for sharing this to me.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 10, 2017, 03:27:58 pm
content: 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

author: Houseman
author_rank: Regular Contributor
timestamp: June 26, 2017, 08:20:13 am
content: Thanks Pal. That's what I was searching for.BIG THUMBS UP!!!!

author: notfaded1
author_rank: Frequent Contributor
timestamp: December 18, 2022, 01:01:58 pm
content: Thanks so much for your post. I have a clock in trying to drive.https://photos.app.goo.gl/uXYj3mYeVZ1H3DP56https://photos.app.goo.gl/jkeiYpx7TqrcX6yX6https://photos.app.goo.gl/UtK5zZrVXXD1QaGu5Bill