urgent help! is there such a "one-push-button" for on and off switch for 240V? - Page 1
Forum section: electronics / beginners

author: drew1900
author_rank: Newbie
timestamp: July 05, 2020, 05:02:42 pm
content: urgent help! is there such a "one-push-button" for on and off switch for 240V?Meaning to say, i can press the same button to turn ON the device, and the same button to turn OFF the device? And also, when the power supply is cut and re-powered back, the device must be in turn OFF mode whether prior before that it was turn ON or OFF (due to safety reasons for my setup)I saw youtube that there were a lot of DIY tutorials to make the circuit. But is there such a circuit (the push button) available to readily buy off the shelf in the market?Any inputs will be greatly appreciated.Andrew

author: djacobow
author_rank: Super Contributor
timestamp: July 05, 2020, 05:07:54 pm
content: Yes. Use the Google to search for "latching pushbutton 240v"

author: themadhippy
author_rank: Super Contributor
timestamp: July 05, 2020, 05:41:53 pm
content: Quotebut that wontQuote

author: Zero999
author_rank: Super Contributor
timestamp: July 05, 2020, 05:52:50 pm
content: Use a latching relay circuit.Is this safety critical? If so, use a safety relay.

author: drew1900
author_rank: Newbie
timestamp: July 05, 2020, 05:54:43 pm
content: hi... yesi do require the feature that it remains power OFF when the main MCB is power off and power back...its similar to most of those 12V devices, where no matter how, you have to first press the ON button to turn the device ON regardless whether power is already feeding in or not...

author: drew1900
author_rank: Newbie
timestamp: July 05, 2020, 05:57:18 pm
content: yes, the safety function is critical! its for a music studio setup that is full automated for rental.. the device is a 240V 2A audio mixer.Is there such a latching relay circuit available in the market? I wouldn't have the confidence to build one from scratch..

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 05, 2020, 05:59:09 pm
content: I feel beginners may want to refrain from meddling with voltages over 50V until they're more comfortable with the basics. The consequences of mistakes are a lot harsher when dealing with mains.

author: james_s
author_rank: Super Contributor
timestamp: July 05, 2020, 05:59:42 pm
content: To do this with a single button I would use a small microcontroller and have that control a relay. If two buttons were acceptable then a simple solution is to use a STDP relay with a 240V coil and use one set of contacts to control power to the coil itself. The "On" button momentarily bypasses those contacts and the "Off" button momentarily interrupts power to the coil.

author: drew1900
author_rank: Newbie
timestamp: July 05, 2020, 06:09:28 pm
content: Quote from: james_s on July 05, 2020, 05:59:42 pmoh yes, two buttons is fine! i'm trying to understand how to wire what you have just suggested..maybe I can suggest another easier alternative, is there a way whereby.... it can be just one switch, (or a knob, or a button, doesn't matter what type), and basically that switch will be reset back to 'OFF' when the main power supply is cut. And when the main power supply is back again, the user will only have to push the switch to 'ON' button in order to turn the device on. I don't require the user to turn the device off in any ways, the device will only turn off when we cut the main power supply.

author: Gregg
author_rank: Super Contributor
timestamp: July 05, 2020, 06:37:56 pm
content: A suitable DPST relay can become a latching relay using the attached schematic. You can get SPDT NC / NO center off rocker momentary switches that could be wired like the two push buttons shown in order to use a single switch mounting. Just make sure that the relay is rated for the voltage, current and is 100% duty; likewise the switch or switches need to be rated for the application.In the schematic shown, A and B closes to keep the coil energized. C and D become the on/off switch for your device.

author: dmills
author_rank: Super Contributor
timestamp: July 05, 2020, 06:54:53 pm
content: Search term "No volt release switch", totally standard thing for power tools and the like.For that application however you might prefer a sequenced power up and down so that things like the power amps go on last and off before the desk powers down, helps to avoid pops and thumps.Regards, Dan.

author: wizard69
author_rank: Super Contributor
timestamp: July 05, 2020, 11:06:59 pm
content: You have me really confused. The audio mixing panel, assuming it is a commercial unit, should have a safe power switching mechanism already. Whatever approach they used should be compliant where the mixer was sold.If for whatever reason the mixing panel doesn't have a power switching unit I'm going to suggest that you get an electrician involved because it appears that you don't have the background to approach this project. As for helping over the net I'm not a big fan of doing so when safety is an issue. There are practices and standards that have to be meant for your local area too.Quote from: drew1900 on July 05, 2020, 05:57:18 pmThe short answer is no! I say that because I have no idea what the local standards are nor why you have a safety issue in this situation. More so if you do have a safety issue why not shut down the entire recording panel?

author: amyk
author_rank: Super Contributor
timestamp: July 05, 2020, 11:39:01 pm
content: What you're describing, especially the two-button type is a control that has been around for many decades e.g. commonly found on machine shop equipment.Quote from: james_s on July 05, 2020, 05:59:42 pm

author: ArthurDent
author_rank: Super Contributor
timestamp: July 05, 2020, 11:41:26 pm
content: You can do it simply with just a Philmore push button SPDT switch #30-1428 that is rated for 10A @ 250VAC. Do a search of suppliers close to you. The switch cost $5-$10USD. This will, however, not drop out if you unplug or lose power.https://vetco.net/products/spdt-push-button-switch-on-on-15a

author: james_s
author_rank: Super Contributor
timestamp: July 06, 2020, 01:31:11 am
content: Quote from: amyk on July 05, 2020, 11:39:01 pmYes I'm well aware of this, they're usually called magnetic controllers in the context of power tools. Purely electromechanical and very reliable.How do you do this with a single button though? You can get a suitable microcontroller for a few pennies, 79c in single quantities if you really want to splurge and get something with flash. You could do the same thing with a toggle flip flop, build something out of discrete transistors or probably a dozen other options but I'm skeptical that anything will be cheaper than a micro and a single transistor.

author: themadhippy
author_rank: Super Contributor
timestamp: July 06, 2020, 02:04:49 am
content: QuoteAnd a relay to switch the load,the power supply and a case to keep it all in .Only off the shelf option i can think of would be a DOL contactor

author: DTJ
author_rank: Super Contributor
timestamp: July 06, 2020, 02:32:57 am
content: I am quite sure you can buy what you need off the shelf.They are used on power tools and machines.Search for 'power fail safe' switch or similar. A workshop I was associated with had all machines fitted with them as part of a safety review.Any industrial electrician should be able to point you to a supplier. It will still need to be wired in.Edit - talk to an electrician and ask him to put an a fail safe relay in an enclosure with an IEC outlet. That way you have a safe stand alone unit. The only down side is someone could potentially unplug and bypass it.

author: drew1900
author_rank: Newbie
timestamp: July 06, 2020, 07:15:27 pm
content: thanks pal!!!

author: drew1900
author_rank: Newbie
timestamp: July 06, 2020, 07:22:13 pm
content: thanks Dan!u r right, ! this is it! life savior!Andrew

author: tkamiya
author_rank: Super Contributor
timestamp: July 06, 2020, 07:24:16 pm
content: It is also called a magnetic switch.https://www.amazon.com/POWERTEC-71054-Magnetic-Paddle-Switch/dp/B01IEM2DSM/ref=pd_bxgy_3/135-8807146-5290626?_encoding=UTF8&pd_rd_i=B01IEM2DSM&pd_rd_r=c7242ebf-a7f0-4281-bcc6-d9b6a7abd5bb&pd_rd_w=Eo6SC&pd_rd_wg=nC1VC&pf_rd_p=4e3f7fc3-00c8-46a6-a4db-8457e6319578&pf_rd_r=A080RM8A9B0BJZYB5QKK&psc=1&refRID=A080RM8A9B0BJZYB5QKK

author: tpowell1830
author_rank: Frequent Contributor
timestamp: July 06, 2020, 08:58:27 pm
content: Quote from: james_s on July 05, 2020, 05:59:42 pmA one button STSP push button switch can do both "on" power and "off" power with a mcu, as you describe, using a state machine in code, default state="off", controlling a relay. The relay coil, of course, would need to be a 5 VDC coil. The contacts need to be rated for 240 VAC. If power failed (or was cut), the mcu would reset with the default "off" condition.EXAMPLE:void setup() {pinMode(outrelayPin, OUTPUT); // sets the digital pin 13 as outputpinMode(inpbPin, INPUT); // sets the digital pin 7 as inputbool state=false; //initialises boolean to falseoutrelayPin=LOW;inpbPin=LOW;}void loop() {digitalRead(inpbPin);if(inpbPin==HIGH)(if(state)(state=false;)else(state=true;))if(state)(digitalWrite(outrelayPin, HIGH); //turn on output 13)else(digitalWrite(outrelayPin, LOW); //turn off output 13)}

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2020, 01:00:38 pm
content: Quote from: james_s on July 06, 2020, 01:31:11 amA quick search through most distributors shows a flop-flop IC is cheaper, than a microcontroller, unless perhaps you're taking about the mega cheep Chinese type, which aren't very begineer friendly.I wouldn't choose an MCU on price, but for convenience and the ability to add more features later, if needs be.