NE555 circuit does it need a switch.
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GerritMax 2 weeks ago
I'm kinda doubting my self on weather this schematic needs a moment contact switch or not in order to work the way I want it to. I need a timed switch that will run a small fan for an X amount of minutes after pressing a button, kinda like with lights in blocks of flats. Press the button and the light goes on for say 5 minutes. Am I correct that I need to place the moment switch on either pin 2 or on pin 8 from the NE555P. Pin 2 = trigger Pin 8 is VCC Project is here [https://easyeda.com/GerritMax/delay-on-timer-230v](https://easyeda.com/GerritMax/delay-on-timer-230v) Dont really want to mess this up as it'll be switching 230 volt.
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JLCPCBsupport 2 weeks ago
Hello ; Yes you need a push button at "TRIG" pin to start the monostable cycle, please to consider that a falling edge should be performed at the TRIG input, means that you need a push button to be wired as follows : ![falling edge.JPG](//image.easyeda.com/pullimage/51M729k6ZpKwvTv9npju0Zf7vCtZlTpuhdkYQuKy.png) Please to read more about "how the 555 timer IC wirks" in the following link (refer to the monostable section) : [https://en\.wikipedia\.org/wiki/555\_timer\_IC](https://en.wikipedia.org/wiki/555_timer_IC) Please to simulate your circuit to make sure that everything is going well.
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andyfierman 2 weeks ago
Before starting your simulation please read - and play with the examples in - (3) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)
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GerritMax 2 weeks ago
I've made the changes [JLCPCBsupport](https://easyeda.com/JLCPCBsupport) suggested but now it just keeps coming with an error. ![easyeda.jpg](//image.easyeda.com/pullimage/K7HVivGZFGeHXRgE0x5dvcDHbDivYZrNYT7efmtA.jpeg)
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andyfierman 2 weeks ago
@GerritMax, That is why I said: **Before starting your simulation please read - and play with the examples in - (3) in (2) in:** [**https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a**](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a) That's not a polite suggestion: it is essential. :) Your simulation doe not run because: You are using components which do not have simulation models associated with them. You have no power supply included in your simulation schematic. Unless you want to model the fuse operation, just replace it in the sim with a low value resistor (about 10mR). You'll need a relay model and edit the parameters to suit your circuit: [https://easyeda\.com/andyfierman/Power\_supply\_decoupling\_and\_why\_it\_matters\_\-451e18a0d36b4f208394b2a2ff7642c9](https://easyeda.com/andyfierman/Power_supply_decoupling_and_why_it_matters_-451e18a0d36b4f208394b2a2ff7642c9) and you'll need these LEDs because the ones in the EELib are for "Educational" purposes and only show the led on/off state whilst inhibiting showing any other time domain data in WaveForm. More general points: Before you spend the rest of your life trying to get your circuit to simulate, you need to consider the following points. Your schematic is poorly drawn and difficult to read. Please see (2.2) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a) You circuit has no decoupling capacitors on the 9V DC output side of U2. These are essential in all electronic circuits. Especially if you are using a bipolar NE555. This shows why: [https://easyeda\.com/andyfierman/Power\_supply\_decoupling\_and\_why\_it\_matters\_\-451e18a0d36b4f208394b2a2ff7642c9](https://easyeda.com/andyfierman/Power_supply_decoupling_and_why_it_matters_-451e18a0d36b4f208394b2a2ff7642c9) I have no idea what you are trying to schieve with the way you have connected R3, C1, C2 and C3. They do nothing except effectively replace C1 with an approximately 50nF capacitor from pins 6 and 7 of U1 to ground (because you've effectively connected a 2.2uF and two 100nF caps all in series). Why have you used two BC547s both connected as inverting stages to drive a relay that the NE555 should be able to drive a suitably specified relay directly from OUTPUT pin 3? In fact your relay drive polarity is inverted. The NE555 output goes high during the timing interval but your 2 transistor inverter pulls the relay coil low when the NE555 output is low. Surely you want to activate the relay coil only during the timing interval? So connect the coil directly from the NE555 OUTPUT pin to ground and use the Normally Open contacts to switch you load on during the timing interval. Both of your LEDs indicate the same state so why use two? Why no LED to indicate that your non-isolated mains input circuit is live?
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GerritMax 2 weeks ago
I take it this means I've finaly got it right? Yes I will also add an led to show when the relay is powered. ![eda.jpg](//image.easyeda.com/pullimage/xiIBhdm9yH30yC5SfK111ozrBI1LxxMKTYUAGYKw.jpeg)
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andyfierman 2 weeks ago
Your sim runs but it is not simulating the circuit you think it is. This is why the Simulation Tutorial runs to over 100 pages with dozens of examples... The switch symbol you have used has no model so it is excluded from the sim. Therefore there is nothing to trigger the NE555. The SPST and SPDT switches in the EELibs are only in fact fixed resistors and so serve little purpose in a simulation. You need to use this: ![image.png](//image.easyeda.com/pullimage/c5sMYxxI2AwLnAYZC4HXbZTqk9MJEGIatLzlPBFY.png) and then drive it from a voltage source configured as a PULSE source to make it operate as a momentary ON switch. There are lots of examples of switches in the Simulation Tutorial. And there's this: [https://easyeda\.com/andyfierman/Setting\_up\_switches\-oW8SPbxTf](https://easyeda.com/andyfierman/Setting_up_switches-oW8SPbxTf) The relay has no model so it is excluded from the sim. Therefore there it shows nothing about how the output of the realy responds to the 555 timer. NE555. That's my fault because I messed up the copy and paste about the relay and the LEDs. Here's the corrected info: ![image.png](//image.easyeda.com/pullimage/8t5YH8ildkE8TwOmOqeYDQAb9rGkh8l1HGkMsVjF.png) ![image.png](//image.easyeda.com/pullimage/7tQGHE2xH7lvEykEEM8XSkQ5lYsrHC8Mbhpyx0S1.png) The 1N4007 must be in parallel with the relay coil not in series, cathode to the +12V supply, anode to pin 3 of the 555 timer. Although decoupling caps usually do not matter in a simulation if the supply rail comes from an ideal Voltage Source, if you have regulator models then you must include them. And as I pointed out above you MUST use them if you have a bipolar technology 555 timer (which the NE555 is: find and read the datasheets for it and run my decoupling caps sims!). You MUST also use a decoupling cap at the input to the 7812 regulator. Again: find and read the device datasheets! If you want to model the fuse, use this: ![image.png](//image.easyeda.com/pullimage/LpdbeTxYpAXHRio7kW94HoEUaLZrEnLmgNquEGg7.png) When you run an LED off the mains it's more usual to connect a diode in antiparallel with the LED rather than in series with it, then the diode does not need to be a high voltage part. R2 C2 and C3 do absolutely nothing in your circuit. Remove them and connect C1 bottom end to ground. Again: read the datasheet for the 555 timer. Please tidy up your schematic: it has no logical flow to it and is messing with my head trying to read it. BTW: the NE555 symbol you have used is horrible because the pin ordering makes no sense in any way: this is a nicer spice symbol: ![image.png](//image.easyeda.com/pullimage/h5PdWcozoHjUNh5ZpiLJBmJ5MB4hgPh3LfNC9nha.png)
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andyfierman 2 weeks ago
Best to do the simulation schematic in a separate project or make sure you remove any simulation specific parts like voltage sources and then switch to Std mode and check that you have assigned all the correct PCB Footprints to the symbols before you try to Convert to or Update PCB.
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andyfierman 2 weeks ago
Drawing your schematic with #FF0000 red wires makes it impossible to see when they are highlighted. Suggest to go back to the default #008800 green colour.
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andyfierman 2 weeks ago
@GerritMax, I have been working on your sim and have found some problems with your design. I have also uncovered some bugs in some of the components. As soon as they are fixed, I will post back and show you a sim that should help you out.
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GerritMax 2 weeks ago
I've actually started again from scratch. Running simulation doesn't flag up any errors either. [https://easyeda.com/GerritMax/delay-off-timer](https://easyeda.com/GerritMax/delay-off-timer)
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andyfierman 2 weeks ago
Enjoy. :) [https://easyeda\.com/editor\#mode=sim\,id=\|4bc62bb77de44e34b534096ab1feca9f](https://easyeda.com/editor#mode=sim,id=|4bc62bb77de44e34b534096ab1feca9f)
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