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  1. D

    Building a sunset dimmer

    OK this isn't working like I expected :) Maybe you can help explain why? From my understanding R3 and C2 set the frequency of the output from U5, U7 then inverts and creates a square wave of the same frequency. R6 and C3 create the reference voltage that U6 uses to vary the duty cycle of the...
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    Building a sunset dimmer

    It seems to be a limitation of the LM324 spice model I downloaded from LTSpice (the model is from National). If I swap it out for a LT6231 that comes with LTSpice it runs fine. dave
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    Building a sunset dimmer

    Now with the file attached . . .
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    Building a sunset dimmer

    Not sure what is going wrong, so I've attached the spice files. Hopefully someone can tell me what I'm doing wrong. thanks, dave
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    Building a sunset dimmer

    OK that is what I suspected. Sorry it's been a very long time since I've done spice :) So I have it starting to run now but get the error: Analysis: Time step too small; time =xxx, timestep = xxxe-15: trouble with 1n4002-instance d1. If I change the cap to make it simulate faster, it just has...
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    Building a sunset dimmer

    I'm trying to simulate a circuit that dims a 12V lamp over a 1.5hour time period. I use LTSpice as my simulator. I need to do the simulation over about 7000 seconds. I set this with a max step size of 1s, but for some reason LTSpice thinks it needs a step size in the us range. It will take...
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    NT1900 as a current limit source

    I have a nte1900 in my circuit hooked up as a current limit source. The connections are VI->30V, VO->31.5ohm resistor->VCCInt and Adj is connected to ground. This should give me ~27V supply that is current limited to 40mA, at least that was my desire. I've noticed that when VCCInt is open...
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    Use LED to denote current flow in AC circuit

    I like that solution. Removes some complexity and reduces components. It routes up easier for my board solution as well. thanks, dave
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    Use LED to denote current flow in AC circuit

    This circuit is just to model the alternating current seen in the legs of the dpdt relay. So I used an alternating current source to model that. Its not a voltage source. Here is the entire circuit. dave
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    555 timer reverse polarity circuit

    It shouldn't matter. He also noted on the schematic that it was for use with a constant current source of 28mA. Looking at your power supply, I don't think it does -30V to +30V, but 0V to 30V. You will need a little different circuit to get that to work. You'll need the use of a dpdt...
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    Use LED to denote current flow in AC circuit

    That is odd, when I click on the attachment it opens up across my entire screen. The images attached are about 1100x770 pixels. I uploaded them to photobucket, maybe this will work better. dave
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    Use LED to denote current flow in AC circuit

    As you can see I'm not afraid to talk to myself. I had to dust off some 20 year old memories and remembered Kirchhoff is your friend. After looking at it that way, I figured I could easily fix this. If I have 40mA flowing through the current, and want to limit the forward bias current in...
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    Use LED to denote current flow in AC circuit

    The problem with this circuit is that all the current (40mA) will go through each LED and that may be too much for the diode. I don't think the current limiting resistor will do anything because the LM317 is going to do everything it can to drive 40mA, well unless I make the resistor so big...
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    Use LED to denote current flow in AC circuit

    Ok after thinking about this (and googling), I think it makes more sense to just put a 1N4148 in series with the LEDs. The spice sim looks good as well. dave
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    Use LED to denote current flow in AC circuit

    All, I'm using this 555 based polarity switching circuit as my base: https://www.electronicspoint.com/555-timer-reverse-polarity-circuit-t250411.html My supply is 30V DC so I'm using a DPDT relay to switch the legs. I'd like to put LEDs in the actual legs to show that everything is truly...
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    555 timer reverse polarity circuit

    I figured out my problem. For some reason LTSpice put the resistor at 2m instead of what I typed, 2M. I can't get it to take M so I used 2000k and it works. thanks, dave
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    555 timer reverse polarity circuit

    Chris, What is the purpose of D1 and R5? I've not seen that configuration on any 555 timer circuits before. I ask because when I simulate it, change the duty cycle for out to something like 90/10. If I remove them it looks just like what you show. Thanks for the schematic, dave
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