Question Can I use ULN2003 to switch 5V relays which in turn switch 220VAC loads? Answer No problem at all. Your ULN2003 choice is good, because it can handle max 150mA, and the most popular, typical 5V relay switch, Songle relay switch, takes only max 70mA. I usually prefer ULN2803 which has 8 …TonyMI’d say the ULN2003A is an antique and not a good choice, nor is the ULN2803. There are much better solutions, though site part recommendation rules prevent me giving examples but they’re a search away. tlfong01@TonyM, Many thanks your for your advice. Would you kindly suggest some words for searching? Much appreciated for updating our old school/outdated knowledge and skills. Cheers. JRE@tlfong01: Your statement about the ULN2803 is somewhat mixed up. ” ULN2803 which has 8 open drain, power NPN BJTs” BJTs have collectors, not drains. tlfong01@JRE, Ah, thank you for pointing out my careless mistake. Errata: “Open Drain” should read “Open Collector”. My apologies to all confused readers. JREThe question and comments don’t mention Songle brand relays. tlfong01406712:05@JRE, Ah, you are right. I didn’t think about that. I did hesitate a second when I use the brand name Songle. I guess Songle is the most popular compared to TongLing which is second. I know even Element14 (Farnell) sells Songle, so it is a good example to use and would not mislead the newbies. On second thought, perhaps I should say for example, “say the Songle relay switch, for example. Thanks again for you help. Cheeers. TonyMYou sound hurt, sorry if you are. Who’s the ‘our’ you mention? tlfong01My apologies for hurting. When I said “our”, I mean me and the OP who I think also is a newbie. Perhaps I should say “*me the newbie and perhaps also the OP“. My apologies for hurting anyone. I did hesitate to say “me”, but then perhaps the OP also wants to update his knowledge. My apologies for hurting any one. Yours sincerely. user263761Can you explain what MCP23017 us? TonyMLooking deeper, I first read both your comments as being sarcastic and mocking…but I’m beginning to think English isn’t your first language and your lengthy comments actually intend to be genuine and sincere. tlfong014067@Nifty, For mcp23017, you can google newbie references from AdaFruit like below: (1) stackoverflow.com/questions/36954218/… (2) adafruit.com/product/732#technical-details (3) learn.adafruit.com/using-mcp23008-mcp23017-with-circuitpython (4) best-microcontroller-projects.com/mcp23017.html. Happy learning. Cheers. user26376112:05@Tony- Yes, Tamil is my first language and English is second and I’m not well versed in it.@tlfong01– Thanks for your info. I learned a lot from you all.Is there any IC like ULN2003 with extra channels? tlfong014067@Nifty 17, You said the following. “Thanks for your info. I learned a lot from you all”. Well I always think we all learn together solving a problem. One of the ways I learn is what is called the PBL – Problem Based Learning. I usually find a EE SE problem and try to say or think aloud how I solve it. Other readers comment on my suggested solution and expand his problem, and I respond by improving my solution. Example, I suggest ULN2083 but you wish a “Many more channels ULN2003 (or MCP23017)“. Your wish is normal, so me newbie engineer will try to entertain your wishes.@Nifty. You said the following: “Is there any IC like ULN2003 with extra channels?” Well, the short answer is No. But it depends on if you are going to use all channels at the same time. If not you can multiplex your channels, using HC138/HC137 3-to-8 selector. If you need to use all channels at the same time, I can also suggest other workarounds.I assume you want many channels on at the same time, then one workaround is DIY your 64 channel ULN2064 as following: (1) Analyse the ULN2003 cct which is actually simple, newbies like you and me can handle it. (2) Learn the free Eagle PCB designer and squeeze as many channels, I mean SMD transistors and fly back diodes on to the PCB. (3) Ask the hobbyist friendly Purple PCB design guy to fab samples to test, (4) Ask your friends if they would crowd fund you to make more samples (and perhaps later make more money with he help of eBay). OSHpark PCB Fab:” oshpark.com. Cheers.