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Forum Index : Microcontroller and PC projects : Flash 3 common catode LED lamps.
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| bob.steel Senior Member  Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I ordered a 4 channel one to check them out $9 AUD about 4 pounds UKP. I also ordered a 4 chanel relay board to try @ $5 AUD . 2 UKP On the SSD it shows 4, the input control signal voltage: (the state of the 0-1.5V low level relay ON) (the state of the 2.5-5V high level relay OFF) So I assume to turn the LED on I take the pin low? then leave the pin high till the next cycle. Would that be wasteful of power? |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
Sure does Bill . Thank You |
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 7817 |
That's what it look like, Bob, but you'll have to experiment. Have you got a link to a pic of the ssd board, preferably with connections showing? Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I don't understand what you meant by this . The arduino puts out 5v so the gate gets 5v voltage gate to source absolute max of 4 volts? I thought you could take the gate voltage to a max of +-20 volts? I don't understand what gate to source threshold means really Its marked as 2v min and 4 v max ? Does it mean I can't use it with the arduino? Edited 2021-07-31 08:10 by bob.steel |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
This is the one I ordered.The chinglish makes it sound pretty damn attractive to something though. SSR ebay Edited 2021-07-31 08:19 by bob.steel |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1638 |
Bob, They look like they AC relays? Bill Keep safe. Live long and prosper. |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
"I don't understand what gate to source threshold means really Its marked as 2v min and 4 v max ?" The "gate to source threshold" is the voltage (between gate and source) at which the MOSFET begins to turn on. In this case it can vary from 2 to 4 V due to manufacturing tolerances. To turn on fully requires a higher voltage, how much higher depends on the current. At almost 1 amp 5V is probably not enough, 6V might do it - 10V will. Logic Level MOSFETs are fully on at 5V. |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
Good day all. I am with Bill again. They look like AC relays which use SCRs not FETs. SCRs need to have the current reduced to zero to turn off. That can mean things like snubbers if the load is capacitive or inductive and so it goes. A DC SSR uses a FET and, quite often, an optically coupled FET. Peter  |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
yeah, I don't know why I said it like that either.  What I meant was: "Your arduino is likely to exceed the worst case for VGSth saturation of 4V so you'll be fine" |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6266 |
If the photo is to be believed, it uses Omron G3MB-202P SSRs 240V AC https://au.rs-online.com/web/p/solid-state-relays/3650737/ Jim VK7JH MMedit |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
You would have to make sure the SSR was of a very specific type. you'd need the luck of the devil to fall on your feet there... send me the numbers for next week's lottery while you're at it  I use the G3MB-202P all the time for switching small mains loads (lights). There are six flavours of it and all but two have a zero-crossing detect in them so they cannot switch a DC load as it expects the switched voltage to be zero(ish) before it will activate - common 100 times a second or more with AC, but totally anathema for DC as you'd need something else to switch the DC into the SSR and trigger the ZCD... G3MB-202PL-4 is missing the ZCD and would probably work, but it is out of spec used like that. Normally switching a DC load with an AC device (i.e. a relay) you have to down-rate to account for the constant power. I would advise you stick with your N-MOSFET as a high-side switch (with the bootstrapping) - you'll have it working by lunchtime. Edited 2021-07-31 15:50 by CaptainBoing |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
G'Day CB. Bob's system needs a high side switch so P channel not N channel or am I up a wattle? I like Bil's / My idea of PNP Darlington and a 4N28 but nobody listens to me  Dunno why Peter Edited 2021-07-31 16:19 by PeterB |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
Hey Peter, you OK? Agreed a P-channel device is the simplest way to do this but suitable devices (e.g. with tiny RDSon) are "rarer" and more expensive. How I wish MOSFETS were more like bipolar where complimentary devices exist for just about any flavour of transistor. You can use an N-MOSFET as a high side switch in two ways (functionally they do the same) You need to have the gate x volts above the source for it to conduct (let's ignore the transconductance curve for convenience and assume it is either on or off). So you either do it with a separate drive voltage which satisfies the requirements, this leads to complications with dual-rail PSUs. Or you can do it with a bootstrap circuit to provide a parasitic voltage for the drive. It is illustrated very specifically in this vid: https://www.youtube.com/watch?v=ZZDdlAgZfvI Edited 2021-07-31 16:52 by CaptainBoing |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
G'Day CB. I am good thanks. I checked the COVID symptoms and got 10/10 but don't have COVID. In fact I had the symptoms before COVID was invented. I don't know how UK prices compare with ours but the BD682? is $2.20 and should be more than adequate (that is until it blows because I forgot something). And I do think (despite what Nancye says) the 4N28 is a good thing to give isolation. Obviously you are on top of the world. Peter |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
LOL don't feel like it. Covid free but feeling like the cat has had me this morning... dunno why, just meh... I mean, what is anyone doing up at 5am checking mails etc?  Loads of options have come from this enjoyable canter Edited 2021-07-31 17:31 by CaptainBoing |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7817 |
Going back to using the mosfets that Bob has a bucket of... How about running a 6v 0.5W isolating dc/dc converter from the 5v arduino supply rail to give 6v above the 28v rail (a 34v rail)? Pull the gate down to the source with a resistor - say 33k. Then the load from source to ground. An opto-isolator (cheap sort) from the 34v rail to the gate to turn the mosfet on. The load will be at around 24v, so the resistor will limit the current through the opto-isolator transistor to about 1mA. The mosfet will get 34-24=10v on the gate. I returned the gate resistor to source rather than ground to (hopefully) stay within the -20v limit. A zener in parallel might be a good idea, but the opto-isolator transistor would need a series resistor then. The mosfets can share the same dc/dc converter. There's very little current as the mosfets are voltage operated, not current. Edited 2021-07-31 18:02 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1162 |
Simplest is this VOM1271 , or equivalent to drive the mosfet, as used in solid state switches, drive its opto isolating input direct from cpu pin; for low speed operation they work a treat. Mike Edited 2021-07-31 18:41 by Solar Mike |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I've set up a test circuit with a transistor and mosfet . The signal drives the tranny and that works fine except it seems to invert the signal so its on when it should be off . Still working on that. Following this circuit Edited 2021-07-31 19:58 by bob.steel |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
Mmm. Im not good at this . I had better get an order in for a DC 4 channel if I can find one . Assumed they were like solenoid relays good for both.Pretty cheap anyway and I have a use for AC anyhow. Have not found anything except maybe 4 of these 4 will cost $20 so getting expensive . Got a lot to make . Edited 2021-07-31 20:48 by bob.steel |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
Bob "4 will cost $20 so getting expensive . Got a lot to make" . Does that mean you are wanting vast quantities or is it just a lot of wiring for a beginner? Peter |
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