Newbie wants some expert advice on a possible chip? - Page 1
Forum section: electronics / general

author: Salmon81
author_rank: Newbie
timestamp: June 30, 2016, 10:52:02 am
content: Hi,I'm new to this site but an avid fan of the eevblog youtube channel.I'm after a bit of advice on a possible chip for a project i'm working on and hoping someone can help me?I've made a pcb for an application using 4 relays, it basically has 2 led's on it and 2 magnetic switches and once a switch is activated it switches one of the led's on (and stays on) and then when the other switch is activated it switches to the other led (and again that stays on)My current design is set up with 4 12v dc relays and 2 12vdc led lamps but i'd also be keen to reduce this to a lower voltage to run off batteries if possible.Hope someone can guide me as to what I could possibly use and apologises if this is in the wrong section.ThanksPaul

author: Rerouter
author_rank: Super Contributor
timestamp: June 30, 2016, 10:58:49 am
content: So essentially you need a latch, here is a circuit i have used before, however you may need to change the resistor values a little, pretty much the led provides a weak pullup holding it off, then when the switch is pressed, it latches on and stays on until power is removed from the led (in my case i was using a microcontroller input with a pullup, to reset it cycled its pullup)

author: danadak
author_rank: Super Contributor
timestamp: June 30, 2016, 11:00:12 am
content: An effective power switch (relay replacement) for low V systemsis a MOSFET, like a logic level MOSFET, many vendors, IR, ST,Vishay, Infineon......http://www.vishay.com/mosfets/Depends on what you are switching, AC, DC, Power, Current....?Regards, Dana.

author: Ian.M
author_rank: Super Contributor
timestamp: June 30, 2016, 11:05:09 am
content: You need to fully specify the problem:-* What is the initial state of the LEDs after powerup if no switches have been activated?* What happens if both switches are activated at the same time?

author: Salmon81
author_rank: Newbie
timestamp: June 30, 2016, 11:06:41 am
content: Many thanks for the reply's already!One thing I forgot to mention is that on the design i've built with relays is designed so that when the magnetic switch momentarilly switched it activates the led then will latch on the last state.Thanks againPaul

author: Salmon81
author_rank: Newbie
timestamp: June 30, 2016, 11:09:50 am
content: Currently on power up both led's are lit but that isn't a problem as that'll only occur from a power cut at the moment as it's running off mains and always powered up, the setup with the switches is in such a way that they aren't able to both be switched at the same time, it is used as a direction indicator so each switch is at opposite end of the application

author: Ian.M
author_rank: Super Contributor
timestamp: June 30, 2016, 11:34:12 am
content: If you don't really care about the powerup LED state, it sounds like a job for a S-R flipflop. These are available as single chips in various technologies and you can even build one out of discrete components (e.g. Eccles-Jordan bistable). Possibly the easiest solution that would permit battery operation would be a CMOS 555 wired as a bistable, but that doesn't have complimentary outputs so one LED would need to be between Vdd and the output and the other between output and ground (both with series resistors of course).

author: Salmon81
author_rank: Newbie
timestamp: June 30, 2016, 11:44:26 am
content: Thanks for those ideas, i'll definitely look into those and have a play with themThanks for your help