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Forum Index : Microcontroller and PC projects : Opto-coupler array?
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9585 |
Hi all. 
Does anyone know if you can get opto-couplers in an array kind of like the NPN transistor arrays? Ideally, I would want NPN-type opto-couplers in one DIL, SOIC or other package. Prefer SMD, but will take DIL if that is all that is on offer. I am wanting to get as many opto-coupled inputs into the smallest space. 4N25's et el, are too big when I need about 62 or so inputs...... I need opto's for isolation, as the buttons to trip the LED in the opto are very long runs - 100 meters or more, and I don't want any RFI or other noise on the lines to the switches, upsetting the MM inputs(read: false tripping), hense the opto's for isolation. Does anyone know if such a thing can be had? I am hunting around the net now, but without a part number to go on, I am not really getting anywhere - just links to single opto's. 
EDIT: I have found some 4-channel ones in SOIC - LINK Quite expensive though, for only four.... I will have a quick hunt around on eBay. EDIT: Should have looked on eBay first, perhaps..... Toshiba 4-channel NPN opto's in DIL, 10pcs for US$3 - LINK ...the search continues... EDIT: Hmmmmm. Perhaps singluar SOT-4 type - they are pretty small, and have a nice price-point - LINK Smoke makes things work. When the smoke gets out, it stops! |
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twofingers Guru  Joined: 02/06/2014 Location: GermanyPosts: 1566 |
Hi Grogster, seems you solved your problem already. I found this from Vishay: Quad Channel, SOP-16, Half Pitch Mini-Flat Package http://www.vishay.com/docs/83687/sfh6916.pdf But I guess this can't beat the eBay offer ... 
Michael causality ≠ correlation ≠ coincidence |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9585 |
Yeah, perhaps I should have looked at eBay right from the off.... 
I found some nice 4-channel NPN SOIC ones here. US$7.50 for ten, or about one buck each in our money, so 25c per opto - pretty good. You can go cheaper if you go DIL, but I think this is the way to go cos I need the board to be as small as possible, yet still have all those opto's!!!  Smoke makes things work. When the smoke gets out, it stops! |
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| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1566 |
Not bad  but don't forget to look in the datasheet.
EDIT: I think that we in Europe 7 EUR to pay only for delivery in most cases (excluded ebay china). 7.50$ for ten is a good deal!  causality ≠ correlation ≠ coincidence |
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panky Guru Joined: 02/10/2012 Location: AustraliaPosts: 1114 |
G, Might a current loop idea work? Lowish value resistor from MM input pin to ground, twisted pair to remote switch and two AAA batteries in series? The switch would only conduct for the brief momentary press so power drain from the batteries would only be low. The twisted pair cable together with low input impedence at the MM input and the line capactance should swamp out most if not all your noise. Just an idea☺ Doug. Edit: You may even get away with supplying the 3.3V from the MM just switching the voltage into the low value resistor at the MM input. ... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it! |
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sparksandsmoke Newbie  Joined: 14/05/2015 Location: IrelandPosts: 12 |
This is what came to my mind, also. A 20mA current loop over twisted pair would be the "industry standard" answer, but I suspect that the components to support 62 inputs may occupy as much space as the opto-couplers, if not more. A multiplexer based solution, perhaps? |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9585 |
@ twofingers - Yep, I have datasheet now, and they seem perfect - I doubt I will get smaller. By their very nature, opto's need a certain amount of physical space to do their thing. @ panky - Interesting idea. I will take it under advisement. @ sparksandsmoke - Yeah, I expect so, now that I have found some 16-pin narrow SOIC opto's. However, worth looking into anyway. Nice member name. Welcome to the forums.
Smoke makes things work. When the smoke gets out, it stops! |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2947 |
Grogster, What about small capacitors in series with the line to the PIC with pull-ups on the external side of the cap. If you are concerned about the spikes the internal clamp diodes should handle them but you could add extra and/or a series resistor to the pic as well. You would only get a spike low for a trigger.. Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9585 |
That's an interesting idea, Mick. Have you done this or are you just throwing an idea into the mix? I like the isolation of opto's though, I have to say, from past experience when I tried to have the PIC pin as the input on the line. I would get false tripping. Back in those days, it was PICAXE and high-level trip, which also was a bad idea. Should have been low-level trip to minimize the aerial effect of the long cable runs picking up RFI which was coupled to the high-impedance input - setup as trip when high - and so it did whenever there was noise on the line, and not when I wanted it to.... Live an learn. The PICAXE forum guys helped me out with a solution to that problem, but I decided right then and there to use opto's in the future. However, your cap idea is interesting - I might breadboard it if you have not actually tried it yourself and can confirm it works like that. Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Hey Grogster, I have had good luck with THESE . I use them with the uMite on one of my little boards... $.065 at qty. 100, not bad. You can see two of them on this board and they take up very little space. I use sip pullups on the output and sip current limit on the input because they are very skinny and take up little space. 
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| circuit Senior Member  Joined: 10/01/2016 Location: United KingdomPosts: 274 |
I think your pricing is out by an order of magnitude; the link shows them to be .65 each at qty 100. ...just when you got me excited! |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2947 |
@Grogs, No I haven't actually tried them, I just put an idea into the mix.. I figure that some RF interference might trigger them but possibly the Opto's could false trigger with the interference as well... I think it is something to try.. You can experiment with various pull-ups and capacitances. The twisted pairs should help eliminate any spikes (providing you kept the wires as pairs.). Incidentally, generally, (at least in Ethernet Comms) NON-shielded provides better noise rejection than the SHIELDED type but in your scenario you could try both types of cat5e cable to see which works best. (GND the Shield ONLY at the Micromite side of the cable run, else you might get earth loops) . I wouldn't use the standard `alarm wire though. Good luck, Sounds like a really decent sensor board you are designing there.. I did look up Element 14 and they list a 4 channel Opto (transitor output) in dip16 for $0.54ea in one off. The picture shows a 4 pin device but the discription states 16pin and 4 channel. Also I have used the PC817 in DIP before, just be careful as there are around 6 different drive currents for the LEDs down to a few mA and upto about 60mA to trigger them.. I got caught with that.. See the spec sheets and ask a question before you buy them. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9585 |
Thanks guys, I will investigate Micks cap idea, but I have some of the eBay opto's coming, so will probably still end up using them. @ viscomjim - cute wee board you have there. What is it? I see it seems to be using one of those MP3 player modules among other things..... Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Hi Grogster, the board is just a simple sound unit with 8 inputs and 1 2A mosfet output that is turned on when the sound is active. One of my friends uses it in his "agritourism" business. He uses it in several different games and such. One also found its way into a pinball machine refurb. Kinda of just a general purpose sound board. I see where you mentioned some long cable runs. I just came across this problem with one of his games. He is using unshielded telephone cable in very long runs and the unit would trigger "wierdly". I'm talking 500' runs here which was not discussed prior to this design. So to get things rolling, I simply added 8 .1uf caps from the screw terminals (inputs) to ground and the unit was rock solid. Triggered perfectly every time. He was using "shock" sensor switches that has an amazing amount of bounce. With the caps, all worked perfectly. Using short runs, ie 50' or less, no caps were needed and debounce was done in software. The board also has the TSOP4838 on board and I2C broken out for expansion (more inputs or outputs) or RTC or OLED as shown in the pic. The 2A mosfet can be used to power 12v stuff like a relay or led strip. It also has a little DC DC converter so it can be powered from 6 to 24 volts without any heat issues. |
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