0
\$\begingroup\$

I want to control 7 AC bulbs using a microcontroller. Only one bulb will be ON at a time. I can do that using 7 relays. But Is there any alternative mechanism or IC that can do that with low cost, less wiring and with saving space?

Remember, I don't need more than one light being turned on, but with relays, any number of lights can be turned on and off; so relays are kind of a waste here.

controlling 4 bulbs using 4 relays and microcontroller; how to replace relays to do that

Optocouplers and TRIAC can be used but it will not be low cost or less wiring than relays.

PS: I'm not a graduate of Electronics Engineering (I'm a Computer Science graduate). I thought it will be helpful to know when you're answering.

\$\endgroup\$
7
  • 1
    \$\begingroup\$ Using DC LEDs , will be much cheaper with a shift register and driver. \$\endgroup\$
    – Tony Stewart EE75
    May 15 at 0:21
  • \$\begingroup\$ @TonyStewartEE75 yeah controlling dc circuit is much easier and cheaper using microcontroller. Controlling AC with microcontroller sometimes becomes a huge pain. \$\endgroup\$
    – TareqNewazShahriar
    May 15 at 0:59
  • \$\begingroup\$ You can also use DC in AC bulbs but there is a surge current 10x same as AC \$\endgroup\$
    – Tony Stewart EE75
    May 15 at 1:02
  • 1
    \$\begingroup\$ Are we talking about AC mains power? How does your insurance company feel about this? Are you in a country with an electrical code? If AC mains, is there any way you can settle for low voltage DC? \$\endgroup\$
    – Harper - Reinstate Ukraine
    May 15 at 4:12
  • \$\begingroup\$ @Harper-ReinstateUkraine yes this circuit will be used with mains electricity. Working with mains electricity is not considered as a crime in my country (yet). But always precautions has to be taken while working with high voltage AC. \$\endgroup\$
    – TareqNewazShahriar
    May 16 at 20:21

1 Answer 1

Reset to default
2
\$\begingroup\$

You can do it with 4 two pole change over relays or just 3 if you have a 4 pole changeover relay available.

Relays 3 and 4 are driven together if two pole changeover ones are used. Four pole changeover relays are not as common as two pole is the reason I suggest that.

It is basically a binary selection tree.

Relay one selects between the first and second group of 4 lamps.

Relay 2 selects the first or second pair within each of those groups of lamps.

Relay 3 and 4 (or just relay 3 if you have a four pole relay available) selects the odd or even lamp from each pair.

Lamp 0 is intentionally missing - select that one so no lamp is illuminated. This is the state with no relays energized.

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
10
  • \$\begingroup\$ Two pole change over relay! I need more time to understand the connection between each relay and microcontroller. One quick question - if it can turn on/off 4 bulbs, then do I need first two relays (relay 1 and 2)? Can't I just use relay 3 and 4 directly with microcontroller? (-was it a silly question!). And are those less or more cost than 7 relays? \$\endgroup\$
    – TareqNewazShahriar
    May 15 at 0:55
  • \$\begingroup\$ @TareqNewazShahriar You can see how a 3-to-8 decoder looks with relays here. I just purchased 4PDT Fujitsu fbr442nd012 relays for USD 1.50 each. So they are not expensive. However, I cannot say they would handle your bulbs as I don't have specific details about them. \$\endgroup\$
    – jonk
    May 15 at 1:01
  • 1
    \$\begingroup\$ Would really be best for the at-rest (de-energized/NC) position to be the empty bulb. \$\endgroup\$
    – Harper - Reinstate Ukraine
    May 15 at 4:14
  • 1
    \$\begingroup\$ @Harper-ReinstateUkraine - Agreed that is a nicer arrangement. \$\endgroup\$
    – Kevin White
    May 15 at 13:24
  • 1
    \$\begingroup\$ @jonk ohoo! I was on the verge of making one. If you hadn't say it, I would have complete it. ;) \$\endgroup\$
    – TareqNewazShahriar
    May 16 at 18:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.