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    555 timer circuit help

    I am trying to build a light lamp that draws about 3 amps at 1.5 volts that uses a 555 timer to trigger it on for about 10 seconds. It needs to also include two LEDs, one green that tells when the lap filament is working and a red one that tells when the filament is broken.

    The power source is around 5 volts and I figure that the lamp itself could be the resistor for the green LED. So far the circuit I have is the positive going to 4 and 8 pin, the 1 pin going to ground, the 2 pin is going to positive with a 100k resistor and a switch going to ground, pins 6 and 7 have a 500k resistor going to the positive leg and a 10uf going to negative for the time period. Pin 3 goes to the bulb and then to the green LED, then connected to ground.

    A few questions: First, should I connect pin 5 with a capacitor to ground? What would be the voltage coming off pin 3? Could it handle 3 amps? Im guessing about 2ish volts to the bulb. I was thinking using a 1.5 volt regulator from pin 3 to go to the bulb. I don't think there is any problem with the circuit to that point. I was thinking of how to trigger on the red LED and turn off the green one when the filament is bad. My guess would be to use two transistors, but not sure how to trigger them.

    One thought I had was to use a relay triggered by pin 3 to draw directly from the 5v in to power a secondary circuit that would be able to better handle the amperage. Still unsure how to make the LEDs trigger in relation with the bulb filament.

    Basically, the circuit is: you push the momentary switch, and it powers the lamp and green LED for 10 seconds (LED indicating that the lamp is lit and working), or triggers the red LED if the filament is broken.

    Any help would be greatly appreciated. Thank you in advance.

    #2
    Re: 555 timer circuit help

    The 555 is a pretty powerful chip but cannot handle 3 amps. IIRC it has a maximum output of about 200mA, and I don't think it can pass that at 5 volts.

    Plus you have that LED in series which means 3 amps must pass through that due to KCL. You'll need a relay or transistor to pass that much current.

    How are you detecting the filament failure? Should the filament failure LED be on, even when the button isn't pressed?

    A schematic would be helpful.

    Comment


      #3
      Re: 555 timer circuit help

      The failure LED would only come on if the button is pushed, so that it either works and shows the green LED, or shows the red LED meaning the filament isnt working.

      I would like to keep it confined to SMD components and make it as small and light as I can. I figured that I would probably need to use pin 3 to trigger a relay to power a voltage regulator to draw that kind of current.

      I was only thinking of using the filament in place of a resistor to save space on a PCB. There are small enough resistors that space would not be an issue. So I guess that after triggered, the power to the filament could be separate from the indicator LEDs. On the negative side of it, could have 2 transistors, one (for green LED) in an on status when the filament is good, but turns off the LED when the filament breaks. One in the off status that when the current on the negative leg of the filament loses power, it triggers the red LED to come on. I don't have a lot of experience in circuit building and especially with transistors.

      Comment


        #4
        Re: 555 timer circuit help

        Are you going to use Incandescent lamp/ You will have to figure out the inrush current due to the cold resistance of the Incandescent lamp. Cold resistance can be 10~15 time LESS than the HOT resistance.
        1.5V lamp with 3A = 4.5W, so the hot resistance will be 1.5V/3A = 0.5 Ohms, so cold resistance will be 0.05 Ohms (at 10 time less), so inrush current will be VERY large!

        BTW: 'I figure that the lamp itself could be the resistor for the green LED' you are not going to be able to force 3A through that small Green LED indicator, you will see nice smoke from the LED.
        Schematic of what you are doing will help.
        Last edited by budm; 08-04-2017, 10:02 AM.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment


          #5
          Re: 555 timer circuit help

          At first guess I don't think there's a simple solution given the (implicit) design constraints...

          - 5V supply for timer
          - use only transistors and other passives
          - lamp is 1.5V 3A
          - use separate 1.5V supply for lamp
          - relay or huge mosfet to switch lamp is acceptable
          - go/no-go lamp check *only after button press*
          - minimum size

          I'm thinking an op amp is needed just because of the low lamp operating voltages involved. Diode drop detections with BJTs aren't acceptable.

          Maybe someone can think of a solution without an op amp or its equivalent circuit.

          Comment


            #6
            Re: 555 timer circuit help

            Having trouble using something to make a schematic. Cant find the components. The one I used before had expired. I will see what I can find so I can post a schematic or just draw it out and take a picture.

            Comment


              #7
              Re: 555 timer circuit help

              "The failure LED would only come on if the button is pushed, " So basically this button is for the lamp test switch, right? If that is the case why not make it so if you push the Lamp test switch and the lamp does not come on then you know you have open lamp circuit?
              Never stop learning
              Basic LCD TV and Monitor troubleshooting guides.
              http://www.badcaps.net/forum/showthr...956#post305956

              Voltage Regulator (LDO) testing:
              http://www.badcaps.net/forum/showthr...999#post300999

              Inverter testing using old CFL:
              http://www.badcaps.net/forum/showthr...er+testing+cfl

              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
              http://s807.photobucket.com/user/budm/library/

              TV Factory reset codes listing:
              http://www.badcaps.net/forum/showthread.php?t=24809

              Comment


                #8
                Re: 555 timer circuit help

                Yep, changing the constraints will make it easier. Using a photodiode or light dependent resistor sensor may simplify things.

                Comment


                  #9
                  Re: 555 timer circuit help

                  Here is a schematic idea

                  Im not constrained to anything in particular other than wanting it to be as small and light as possible. Keeping it to SMD components and the board as small as possible.
                  Attached Files
                  Last edited by garry7263; 08-04-2017, 12:58 PM.

                  Comment


                    #10
                    Re: 555 timer circuit help

                    The idea is to push the button and have the light come on for 10 seconds, with a green LED indicator to tell if the lamp is lit. If the filament is not working, the red LED will indicate that the filament is not working (broken). The light is actually a glow plug on a radio controlled helicopter. Just push the button and it lights the glow plug for 10 seconds to give me time to hit it with the starter. The reason for the LEDs is so that if the filament in the glow plug is good, it will light green and if it isn't, it lights red (letting me know I need to replace the plug without having to pull the plug and check it visually).

                    I want to use a timer so that I can draw off the receiver battery but have it turn off on its own so there is no chance of forgetting to flip a switch manually for fear or draining the battery needed for controlling it.

                    I use the term "light" because basically it is the same thing. I am going by 3 amps on what others have said glow plugs draw. The voltage is nominally 1.5v to keep the filament from burning out (though some use 2.0 volts), so I think a regulator would be the best way to step down the voltage. Maybe using diodes to lower it to a safe 1.5v? I have seen some 1.5v 5 amp SMDs (or maybe a 1.8v). I am sure there are multiple ways this could be done, its just trying to keep it as small and light as possible.
                    Last edited by garry7263; 08-04-2017, 01:12 PM. Reason: wanted to add some comments to what was written previously

                    Comment


                      #11
                      Re: 555 timer circuit help

                      What is S1? Is it a optoisolator? If you actually want to light up the light bulb, 3A needs to pass through the bulb, and by KCL, 3A needs to pass through S1 +/- terminals because it's in series. As budm indicates, and if it's an LED in there, it will smoke as its resistance is higher and thus all the voltage will drop across it instead of the bulb you want to light up. (actually it probably won't smoke with only 1.5V... but that's still a problem as your light bulb won't light.)

                      As said, without using op amps, I don't think there's really anything that will have low enough drop in series with the light bulb such that it will have 1.5V and still have enough voltage to turn on an LED.

                      As you draw there:
                      S1's +/- will take the whole 1.5V. It will not pass enough current to light the bulb. Lamp will be always OFF.
                      Thus S1 will be on whenever relay 1 is on, the Green LED will be on when relay 1 is on, as long as the bulb filament is intact.
                      Relay 2 will be on whenever relay 1 is on and hence LED2 will always be on when relay 1 is on.
                      Last edited by eccerr0r; 08-04-2017, 01:09 PM.

                      Comment


                        #12
                        Re: 555 timer circuit help

                        S1 is a voltage controlled switch

                        My thought was that when the timer is on, it switches relay 1, sending current to the Voltage regulator and completing the circuit to light the glow plug and the the green LED (which is turned on by the voltage going through the switch. When that circuit is active, it operates relay 2, which turns off the red LED ( normal state is on so when the light circuit is active, it is off, and when the light is dead, the relay goes back to the on state.

                        I dont know how to use an op amp. I am more of a troubleshooter. I can find bad parts and repair them, but not very good at designing circuits.

                        Comment


                          #13
                          Re: 555 timer circuit help

                          No guarantees but this has the general concepts that should do what you want from the initial design requirements.

                          Note that it is still not using the bulb (R3) as the sense item, it requires an external sense R4, and yes it's only 0.047 ohms.
                          Attached Files

                          Comment


                            #14
                            Re: 555 timer circuit help

                            I redrew it more or less to figure out the current flow.

                            -Only using half the op-amp? It is 3 volts in total I assume.
                            -I noticed the cap from pin 5 to ground.
                            -I am guessing that K1 is a dual relay.
                            -I put in the 1.5v regulator as I assume that the 1.5 volts was a separate power source. Maybe put a diode inline to keep flow back to the rest of the circuit?
                            -The bulb pulling current along with the resistor R8 restricts the threshold to the transistor?
                            Attached Files

                            Comment


                              #15
                              Re: 555 timer circuit help

                              -It's not "half" it's one... the IC has two in it.
                              -It's not strictly necessary to put a cap on the control voltage pin of the 555
                              -KiCad didn't have a SPST relay, only a DPDT, so you get the picture...
                              -Look very carefully how the power is connected, yours is connected wrong.
                              -R8 is just there to prevent killing the LM358's output. Its value isn't very critical.

                              I changed it a bit, I always end up cheapening the circuit ... why do I do it I don't know... Maybe...
                              Attached Files
                              Last edited by eccerr0r; 08-04-2017, 07:55 PM. Reason: new improved schematic with smaller BOM

                              Comment


                                #16
                                Re: 555 timer circuit help

                                Think what you need to consider when building the circuit: you write thins down one by one and see how to accomplish each requirement.

                                1) 5V power source and the load requires 1.5V @ 3A, so the Voltage regulator will have 5V - 1.5V = 3.5 V drops on the regulator, so power dissipation for the 1.5V regulator will be 3.5V X 3A = 10.50 Watts of wasted power. If your power source is battery then you are just wasting lots of power for nothing, any device in series with the load will have dissipate that power to drop 5V down to 1.5V.
                                You should look into something like this:
                                http://www.ebay.com/itm/5A-power-75W...item4621fc2b7d

                                2) You already have Green LED indicator that will show you if the filament, wiring, regulator are OK or not, if the filament is bad then the LED will not light up, so just label the LED as 'Filament OK' indicator, if it does not light up when you press the start button to start the timer then you know you MAY have problem with the filament, the wiring to the filament, or bad 1.5V regulator. Why would you need the Red LED to tell you if the filament is bad.

                                Timer module:
                                http://www.ebay.com/itm/DC-5V-12V-Ad...item1c6a3ddb70
                                Last edited by budm; 08-04-2017, 09:02 PM.
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment


                                  #17
                                  Re: 555 timer circuit help

                                  This is actually what I am trying to make. But I am too broke, and cheap to spend that. Plus I want to try to build my own. Many of the onboard glow circuits go for $25-$100. My needs are more simple. I just want to push the button to turn it on and have it be on for 10 sec at a time to reduce the possibility of burning out the glow plug and not drain the battery, and just to have an indicator to know if the plug got burnt.

                                  These other circuits have the ability to turn them off and on from your transmitter, or to have them operate at low throttle when you are dumping more fuel in the carbs that sometimes chokes them out and stalls them. I have one of those for a twin cylinder motor I have, but for the helicopters I have, I just need a simple circuit and have it with the smallest footprint and lightest weight possible.

                                  Here is one of the cheaper ones:
                                  Cheap Chinese Glow Driver

                                  The larger and more elaborate one:
                                  Sullivan Onboard Glow Driver

                                  Or this one:
                                  Programmable Onboard Glow Driver

                                  Basically the only change in the Chinese one is that I don't need to be able to operate it from my transmitter and I want an indicator to show that it is on and working or that there is a problem with the plug. I was thinking I could integrate the button on the PCB, and have the two LEDs at the end so when covered with clear shrink tubing, it would be easily visible. It will be going on helicopters so having the end of the PCB hanging from the edge of the canopy is not a problem.

                                  Comment


                                    #18
                                    Re: 555 timer circuit help

                                    Well you are going to solve power problem which I already explained.
                                    Do you mean you cannot spend about $10 for those two modules on Ebay? If that is the case I do have cheaper solution for you.
                                    Just added up all your parts and see how much it will cost.
                                    Last edited by budm; 08-04-2017, 10:54 PM.
                                    Never stop learning
                                    Basic LCD TV and Monitor troubleshooting guides.
                                    http://www.badcaps.net/forum/showthr...956#post305956

                                    Voltage Regulator (LDO) testing:
                                    http://www.badcaps.net/forum/showthr...999#post300999

                                    Inverter testing using old CFL:
                                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                    http://s807.photobucket.com/user/budm/library/

                                    TV Factory reset codes listing:
                                    http://www.badcaps.net/forum/showthread.php?t=24809

                                    Comment


                                      #19
                                      Re: 555 timer circuit help

                                      Also, the idea behind the indicator LEDs are to let me know when the device is putting a drain on the battery weather the plug is bad or not. On the cheap Chinese one, (in the pics) you can see there is not much there, and that has the ability to be activated with the transmitter. So I am just interested in losing the remote button/LED and opting for two LEDs on the end with a tactic momentary switch, and losing the transmitter control circuit.

                                      The programmable one is just way to large and heavy. I have one like the Sullivan one for an OS FT1.60 twin, but that too is too much for what I need for a heli, but on a 1/4 sized CUB, that wont even notice the weight.

                                      Comment


                                        #20
                                        Re: 555 timer circuit help

                                        Dang, you should have said heater from the get go, then it would give a good reason why you can't see the heating element.

                                        Also this is a heater and you probably don't care that much about the exact voltage so some drop is OK. Also a relay is not necessary, a logic level MOSFET will also work if not better and smaller than a relay.

                                        Comment

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