What are my options to generate a 28V amplitude square pulse, 15 ms duration? - Page 1
Forum section: electronics / beginners

author: raz2701
author_rank: Newbie
timestamp: May 07, 2025, 03:54:15 pm
content: I have an SP4T switch, latching, that in order to open/close a channel it needs a 28V, 15 ms long pulse to actuate. I have an arduino uno that I was thinking I could use alongside a 15 ms delay() call before turning off.Problem is two-fold, I need to be able to send both positive and negative 28V in order to open/close the switch, and the arduino digital pin can only do high/low as far as I understand.The second problem is how do I go from 5V to 28V? Is there an IC I can hook up to get the level higher?Should I even bother with an arduino since I don't think it can do +/- voltage output?At the core the question is what's a simple, robust way of sourcing a +/- 28V pulse that lasts 15ms? I will ultimately want to have control over which one of the four channels I want to open/close, so I need a microcontroller for the finished project.Any ideas?

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 07, 2025, 04:02:36 pm
content: You can switch a N-channel mosfet with the Arduino board. The mosfet can take care of the 28V. Needing both positive and negative makes it a bit harder though.Search the net for "arduino switching a n-channel mosfet" to find more on how to do this.Do you have more information on the SP4T switch, like make and model. Depending on how it can be connected, maybe a H bridge can be used to make the positive and negative pulses.

author: langwadt
author_rank: Super Contributor
timestamp: May 07, 2025, 04:06:59 pm
content: what current?

author: raz2701
author_rank: Newbie
timestamp: May 07, 2025, 04:22:39 pm
content: It's this switch:https://radiall-files.s3.amazonaws.com/tds/ramses/R583423141.pdfI was wrong it's SP6T.The only current spec I see is listed at 62.5 mA.

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 07, 2025, 05:25:03 pm
content: That is a very special switch to say the least.I suppose it is possible to control it using 6 H bridges, but care has to be taken to only activate them in such a way that there won't be any shorts on the shared connections.The 62mA is a low current, so no special needs there, but the 28V makes it that you need "proper" H bridges. Something like this one is a bit overkill, but shows what I'm talking about.https://www.ti.com/lit/ds/symlink/drv8829.pdf?ts=1746561432206&ref_url=https%253A%252F%252Fwww.google.com%252FInstead of connecting a motor to the outputs you connect a coil. This allows you to pulse the coil both positive and negative. Each coil needs it's own H bridge, but because two coils share a common lead make sure the two bridges connected to this shared lead are putting opposite supply rails onto this lead.

author: Benta
author_rank: Super Contributor
timestamp: May 07, 2025, 06:47:26 pm
content: That certainly needs a complex drive.The <15 ms specification is not for the drive signal, but indicates how fast the switch opens/closes mechanically.The drive signal just needs to be long enough to move the plunger and latch it, prolly around 100 ms.

author: tooki
author_rank: Super Contributor
timestamp: May 07, 2025, 07:39:18 pm
content: Quote from: raz2701 on May 07, 2025, 03:54:15 pmJust FYI, though fundamentally irrelevant to your situation: actually, no, Arduino outputs aren’t just high/low. Every Arduino GPIO is tristate, meaning you can put it into a high-impedance state. (You do this by setting it to be an input.)And for many applications you can use PWM to output pseudo-analog without needing a DAC.

author: dzwer
author_rank: Contributor
timestamp: May 07, 2025, 07:44:43 pm
content: Yes, a very special latching relays.If you want to control every section independently you need a 3-state half bridge at every power(control) input and complicated algorithm of operation.Or in other words, for every power(control) input you need Enable and Direction control.Also on power-on of the device you have to initialize the state of all actuators.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: May 08, 2025, 03:45:19 am
content: Is it really negative voltage or just reverse polarity to switch the latch? If only reverse then use two outputs and two regular relays to drive your latch relay.

author: Ian.M
author_rank: Super Contributor
timestamp: May 08, 2025, 05:59:56 am
content: It doesn't need tristateable drivers. Drive all the 'Power input terminals' (coil pins) either high or low as the idle state and no current flows through the coils, even when you swap from all high to all low or visa versa. Pulse all the coil pins on one side of a specific coil to the opposite state to the rest to set or reset that actuator, depending on which side is high.To drive it with 'jellybean' or junkbox parts, I'd use a ULN2003 controlled by a single MCU port so you can toggle groups of pins simultaneously, with a pullup resistor and NPN emitter follower per output, with an antiparallel diode base to emitter so the ULN2003 can actively pull down the emitter. I'd use a 29V supply to allow for voltage drops in the drivers. Don't forget to connect the ULN2003's common cathode of its internal clamping diodes to the positive supply. No low side clamping is needed due to the emitter followers.You could also use a pair of L298N H-bridge ICs with all enables tied to logic Vcc, as quad independant push-pull drivers, but that would need external clamping for both high and low side. Don't attempt to use a 'smart' H-bridge with active current limiting.No doubt there is a better single source octal or quad push-pull 30V driver IC, that someone will now suggest.

author: neillnz
author_rank: Contributor
timestamp: May 08, 2025, 10:02:35 am
content: You should be able to find a suitable multiple channel half bridge driver, however they tend to be in tiny packages.If you want to take an old school approach you could check out the R&S CMS service manual:https://elektrotanya.com/rohde_schwarz_cms-52_sm.pdf/download.html#google_vignetteThe CMS was/is a radio test set, the step attenuator used latching relays.The schematics on pages 458 & 459 show the drivers used which take a TTL logic level pulse to drive the latching relays in the step attenuator.

author: xvr
author_rank: Frequent Contributor
timestamp: May 08, 2025, 10:53:34 am
content: Quote from: pcprogrammer on May 07, 2025, 05:25:03 pm7QuoteDRV8718S will be better (only one IC will be needed)

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 08, 2025, 11:21:07 am
content: Quote from: xvr on May 08, 2025, 10:53:34 am6 coils, so six full H bridges will do.Quote from: xvr on May 08, 2025, 10:53:34 amThis fits with Ian.M his suggestion of using basically half bridges. This indeed is enough to make it work, and I concur with that. In this case you need 7 of the 8 half bridges the DRV8718S has.It eliminates the risk of shorting parts of the full H bridges, I was thinking about.As with lots of developments, there are more ways to get a satisfying result.

author: Ian.M
author_rank: Super Contributor
timestamp: May 08, 2025, 11:57:55 am
content: The DRV8718S is an eight channel half-bridgegatedriver, which means you'd also need 14 external N-MOSFETs for this application using seven of its channels. I see little benefit over two quad half-bridges with internal MOSFETS.

author: langwadt
author_rank: Super Contributor
timestamp: May 08, 2025, 12:00:45 pm
content: a few of these,https://www.lcsc.com/product-detail/Relay-Coil-Drivers_GATEMODE-GM8023A_C269870.html

author: xvr
author_rank: Frequent Contributor
timestamp: May 08, 2025, 12:06:37 pm
content: Quote from: Ian.M on May 08, 2025, 11:57:55 amYou are right. I confused it with DRV8908, sorry. DRV8908 is 8 half-bridge drivers with 1A current.QuoteBut these 6 coils connected in series, exposing 7 pins in total. All of them should be driven independently, so 7 H bridges.

author: langwadt
author_rank: Super Contributor
timestamp: May 08, 2025, 12:09:24 pm
content: Quote from: Ian.M on May 08, 2025, 11:57:55 amdon't know about that specific one but plenty of gatedrivers could easily drive the ~60mA directly, it's just that most of them (like 442x) are limited to <20V

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 08, 2025, 12:10:33 pm
content: Quote from: Ian.M on May 08, 2025, 11:57:55 amWhoops, missed that one.Quote from: xvr on May 08, 2025, 12:06:37 pm7 half bridges not H bridges. A H bridge consists of two half bridges to make up a full H bridge.