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Non inverting Schmitt Trigger question
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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
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Re: Non inverting Schmitt Trigger question
Originally posted by Longbow View PostYour description of the power windows is interesting. Depends upon how many functions are already controlled by the main computer. How much of the logic is local (inside the door itself)? All this logic CAN be implemented locally, but I would first ask if there is something faulty with the present setup?
Another example is a powered antenna. My car has a local circuit attached to the motor. That circuit assumes that the antenna is in the down position when the car is shut off. In this case, the antenna is either all the way up, or all the way down. For your window, it seems like the motor should only be required to close the window when you lock the car, regardless of where the window might be. So the direction would only be "up". If the window is already all the way up, then the stall circuit will detect it.
Since there is no mechanical limit switch, the up and down limit is a circuit that senses the stall current in the motor, and then shuts it off.
If I have the antenna assembly on the bench, the measured inrush current is not an issue because the motor is relatively small and geared down. The circuit is designed to detect the limit condition by sensing a current peak that lasts for a certain length of time. The stall event can last as long as your design says it should for reliable detection. So, including special circuitry to detect startup (inrush) current is unnecessary. There is no micro on that board, either. Just a couple of relays and a few discrete transistors and other parts.Wattevah...
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Re: Non inverting Schmitt Trigger question
Oh yeah, the reason I want an H-bridge is because I thought while we're at it, I might as well add that "latch" function that other cars have, whereby if you press the rocker in one direction and hold it there for a little, the window will go down/up by itself without you having to hold the button down - useful in summer when you hop in and want to buckle up at the same time. I've already simulated this and it works, though building the thing will be.....interestingWattevah...
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Re: Non inverting Schmitt Trigger question
Originally posted by Dannyx View PostThe shortcoming is the one in my previous posts: while it DOES work, sometimes it doesn't roll them all the way up, since it doesn't actually know whether the window has closed or not, so if there's a smudge or something sticky on the window or rubbers or for some other reason the window takes longer to roll up, the box will cut out even if it's not up yet
Here is an interesting article on start and stall dc motor current. As you can see, the stall current is actually greater than the maximum start current. The stall current is steady state, whilst the start current is a short pulse (depends upon the load).
Your particular application is relatively simple because you don't care too much about speed. The load is fairly constant and the duty cycle of each event is short. The automatic closing circuit always runs the motor in the same direction (to close the window). So you don't need a fancy H-bridge, just a relay or a single control FET.Attached FilesLast edited by Longbow; 06-24-2017, 08:43 AM.Is it plugged in?
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Re: Non inverting Schmitt Trigger question
Originally posted by Longbow View PostIf you think about it, the premature cutout is due to the current level sensing in your circuit. The design current limit is set too low for this particular job. It isn't a reliability problem at all. In fact, the circuit is working very reliably. Since it is already built, all you have to do is find out how the current sense/current limit is set and change the part values a little. You would be doing the same thing starting from scratch.
Here is an interesting article on start and stall dc motor current. As you can see, the stall current is actually greater than the maximum start current. The stall current is steady state, whilst the start current is a short pulse (depends upon the load).
Your particular application is relatively simple because you don't care too much about speed. The load is fairly constant and the duty cycle of each event is short. The automatic closing circuit always runs the motor in the same direction (to close the window). So you don't need a fancy H-bridge, just a relay or a single control FET.Wattevah...
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Re: Non inverting Schmitt Trigger question
Quick update: admitting I go with the simplest P-N channel MOSFET H-bridge, would THIS schematic be good for the purpose ? Don't mind the FETs themselves, they will be different and suitably sized to handle the rush and stall currents of the windows - it's the drive I'm interested in, namely those 2 BC547 transistors. In my setup, since I will not have 4 individually addressable output pins, just a 12v and GND pin, I'm thinking of tying A and D together and B and C together. That way, when AD goes HIGH, the bottom left FET will turn on (since it's N channel) and the NPN on the right will pull the gate of the top-right FET to GND, also causing it to turn on. We've now got current flowing "top-to-bottom" and the motor turns in one direction. To make it go the other way, BC goes high and the mirror image of what I previously said applies. To stop it, all inputs go to GND. Would this circuit work for our purpose ? One thing that's vitally important is very low stand-by power consumption (since absolute zero idle current is obviously not possible), because this thing will be in a car, meaning battery power....the car might not get started for as much as a week to charge the battery, so I wouldn't want to come back to it one morning only to discover the battery is flat and I have to push the damn thing I have a separate car battery I'll use to run extensive tests on the bench before even daring to bring it near the car, so we don't have to worry about that just yet.Wattevah...
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Re: Non inverting Schmitt Trigger question
You need to consider dead-time in H-Bridge also.Last edited by budm; 06-27-2017, 08:56 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
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Re: Non inverting Schmitt Trigger question
Originally posted by budm View PostYou need to consider dead-time in H-Bridge also.Wattevah...
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Re: Non inverting Schmitt Trigger question
When you turn off the FET they do not turn off right away due to GATE capacitance of the MOSFET, you will need to the scope circuit to look at the switching action.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
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Re: Non inverting Schmitt Trigger question
Originally posted by budm View PostWhen you turn off the FET they do not turn off right away due to GATE capacitance of the MOSFET, you will need to the scope circuit to look at the switching action.Wattevah...
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Re: Non inverting Schmitt Trigger question
At this point, a block diagram of your design is needed. Obviously, the timer approach to window closure is not the one you want. I am unclear on whether you have discarded the car's stock circuit completely? In that case, control of both directions is needed so an H-bridge will do the job. It isn't necessary to re-invent the circuitry for this motor control application since dozens of IC's exist that will do what you want. Bi-directional control of a d.c. motor is a standard industry application so you won't be needing much more than a few peripheral parts. I'm sure that some of the chips have a current sense feature, so all you need is a measurement of motor run and motor stall current to make the chip work with your window motor. Scrap the timer.Is it plugged in?
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Re: Non inverting Schmitt Trigger question
Originally posted by Longbow View PostAt this point, a block diagram of your design is needed. Obviously, the timer approach to window closure is not the one you want. I am unclear on whether you have discarded the car's stock circuit completely? In that case, control of both directions is needed so an H-bridge will do the job. It isn't necessary to re-invent the circuitry for this motor control application since dozens of IC's exist that will do what you want. Bi-directional control of a d.c. motor is a standard industry application so you won't be needing much more than a few peripheral parts. I'm sure that some of the chips have a current sense feature, so all you need is a measurement of motor run and motor stall current to make the chip work with your window motor. Scrap the timer.Wattevah...
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Re: Non inverting Schmitt Trigger question (+circuit)
Here is the (still crude schematic) of the current sensing circuit I envision. You can simulate it here. Just go to "file", select "import from local file" and load the TXT file I provided (let me know if it works). Now please bare with me as I'm sure it lacks a lot of things and there are probably many others wrong with it and my idea (no filter caps anywhere for example - I know), but that's precisely the point: to polish it and make it work
This is just the current sense part - I'm still working on the latch and stop circuits which will turn on the circuit when the car is locked, latch it on (since the lock signal is only present for a brief moment) for as long as necessary and then stop it once the window is closed.
I'll walk you through: in lack of a proper motor piece, I simulated it using a potentiometer on the left: as the motor halts, it will draw more and more current, which can be simulated with that pot....FAR from ideal, but it got the job done in the simulator. The current shunt resistor is a 0.05 Ohm (50 mOhm) resistor, which I imagine is STILL too high for a motor that draws as much as 20-25A when locked, but I chose it because I'm planning to test this out on the bench and the only thing I have handy are some 100 mOhm resistors which I'm going to parallel to drop to 50 mOhms and see if I at least get a reading with that drill motor I told you about.
Anyway, regardless of what this resistor is going to be, its output will be far too low to drive anything, so it MUST go through the non-inverting op-amp amplifier represented by U1. Here's where the math starts: I've also included that excel calculator with the actual values used in the simulation. The numbers (and Dave from EEV ) tell me that amp has a gain of 11 in this configuration...which it does: 0.1v in results in 1.1v out (the graphs at the bottom of the simulator also show this pretty well: if you move the pot around, as the "load" increases, so does the output of U1).
The output then goes to the main event: the schmitt trigger represented by U2. After MANY hours spent calculating and researching, I put together the excel calculator to simplify my work and played around with the values to get them as round as possible and used them in the simulator. It works to a degree, but the upper threshold is off: the numbers tell me it should be 2.2v, however I need to crank much higher than that (to around 3v) to get U2 to trip over. The lower threshold works fine though: when current drops enough, the non inverting input of U2 also drops down and when it reaches around 1v, U2 turns off like it should. It could be a simulation error though...let me know what you think and by all means feel free to play around with it and post it back CheersWattevah...
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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
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Re: Non inverting Schmitt Trigger question
Originally posted by budm View PostWattevah...
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Re: Non inverting Schmitt Trigger question
You also get common mode rejection too. Car is noisy environment for electronics.Last edited by budm; 06-30-2017, 12:01 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
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Re: Non inverting Schmitt Trigger question
This might be a stupid question, but I don't understand in the article budm provided why the negative supply rail (VSS let's call it) of the op-amp is not connected to GND, but instead to the zener diode and resistor. I know how that zener operates - it regulates to 5.1v and the resistor prevents too much current from flowing and burning the zener (though I would've placed the resistor at the cathode, correct me if I'm wrong). Now let's If I have 12v as "Bus voltage" and the zener is 5.1v as the article says, what would the supply for the op-amp be ? 7v ? The article DOES explain the purpose of the zener further down, but it throws some pretty fancy terms around, mainly common-mode voltage which I can't possibly grasp for some reason Other than that, it's just "simple" mathWattevah...
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