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Switching Led

Discussion in 'General Electronics Chat' started by willeng, Jul 4, 2014.

  1. willeng

    willeng Member

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    Hi Kiss,
    .082uF is correct isn't it.

    Ct= C1 x C2 / C1 + C2
    C1 x C2 = .1 x .47 = .047
    C1 + C2 = .1 + .47 = .57
    .047 / .57 = .082uF

    Not really sure how you can't see the Ampltude changing?

    I think your having a dig at me!

    Cheers
     
  2. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    .47uF in series 0.1uF


    Get in the habit of using leading zeros

    1/Ct = 1/0.47 + 1/0.1
    1/Ct = 2.13 + 10
    1/Ct = 10.213
    Ct = 0.469 uF ... and it's lower than the lowest valued component.

    In Parallel, you get 0.57 uF
     
    Last edited: Jan 16, 2016
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Do you think it's basically working?

    Is the sine wave anomaly at 18 s basically the triac going open and your picking up hum?

    Are you looking across the minimum primary load?

    e.g. transformer + load + probe + circuit?

    So, when the triac opens, the probe sees the xformer and load and the probe is loaded.
     
  4. dave

    Dave New Member

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  5. willeng

    willeng Member

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    Hi Kiss,
    Sorry for the delay each time, every time I get back to the site I have to log in & for some reason I can't get to the log in page, it takes many tries to get it?

    When I turn the pot into the Arduino Down I can get the voltage from the triac down to around 25V Ac but then near total zero of the pot the triac output jumps to 40V Ac output, hence the sine wave in the video at zero input from the pot.
    If I change the cap as mentioned it changes the amplitude of the triac output when the pot is totally off.
    I don't think it's hum due to the fact of the amplitude of the output when changing the cap value.

    I have the Triac connected directly to the primary winding, the secondary winding has the 100uF cap & the 6Ω resistor as the load.
    The probe is connected to the Active leg on the primary side of the transformer, ground clip to Neutral .

    Cheers
     
  6. willeng

    willeng Member

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    Hi kiss,

    Somebody Turned up so I cut my explanation a bit short before, sorry.

    The circuit works very well to 240V output, it's only the issue at near turn off of the pot into the Arduino where the Voltage from the Triac continues instead of being OFF.
    By changing the cap values the triac output varies. The Triac is being triggered on by something instead of turning off, there is no gate signal when this is happening.

    At the moment if I turn on the mains power to the circuit the Triac output is 40V without a gate signal being applied ( Arduino Off--Disconnected) but the Triac is still being Triggered?
    Before with a different cap value the output of the Triac was much higher & you could here the transformer working with no gate signal or power to the Arduino, just the mains turned on to the Triac Circuit.

    Cheers
     
  7. willeng

    willeng Member

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    Hi Kiss,
    I found the problem:
    I had a BTA16 Triac in the circuit which has dubious ST markings on it like I mentioned before so I tried another & another with the same markings with no luck.
    I then went down to my Flow Test bench & removed an original ST BTA16 from the circuit & tried it in this & presto I can adjust down to 33mV & no sign of the sine wave at pot switch off.
    This had me buggered for quite a while, I know I don't know much but I could find no reason for the issue?
    It is now working beautifully!

    Cheers
     
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Under the weird conditions what's the trigger signal voltage? R11 to ground. Not probed on the LED side?

    ==

    Well I guess you can ignore that. So, you've ALMOST tackled this project?

    Is PID next?
     
  9. willeng

    willeng Member

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    Hi Kiss,
    Yes, very excited now actually.
    Yes now the biggy, PID.

    I have just been trying to work out something suitable to control on the bench, I have an idea but have to go & have a look at what I have to set it up properly.

    Almost Tackled this project?
    I wish, I still have the BCD Switch problem I was having to overcome & many more things that pop into mind.
    One thing at a time though, I will try to control something first with the Transformer on the bench to see how I go.

    What are your suggestions as to what to control?

    Cheers
     
    Last edited: Jan 16, 2016
  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    One thing is open loop control of a universal motor.

    All of the PID stuff that I did that operated into a transformer required current limiting, but the currents were pretty high.
    All used back to back SCR's. The SCR units were 2.5x oversized and the fuses were one EXPENSIVE one on the SCR unit and one cheap one.
    Shorts were somewhat common events, but blowing a $1.00 fuse was preferable to blowing a $35.00 fuse.

    Fuses to protect SCR's/Triacs are know as semiconductor fuses or I2t fuses.

    So, I don't know if you will need current limiting or I2C fuses

    We did a lot of it, until I put my neck on the line and said, this is ridiculous.

    Instead of a custom panel that:

    Didn't read power correctly with analog meters, but they were able to monitor the process.
    A custom panel with a Variac, Voltage and current meters and sometime a temperature readout that tool up a HUGE amount of space I suggested a 1 RU (Rack Unit) DC power supply and a ramp/soak controller. SO about $2500 USD per source. Typically we required up to seven power supply systems per research unit.

    We had to upgrade to something because the outputs of the controllers were becoming standard (i.e. 4-20 mA) and not proprietary.

    It would have been nice to have a "power readout", but we didn't have that anyway.

    In one case they wanted true power and I found a 3 phase power meter that would operate at low voltages and they used that for 1 source.
     
  11. willeng

    willeng Member

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    Hi Kiss,
    Just one question before I forget, with back to back SCR's as you have mentioned, do you fire one SCR for the Positive half wave & then the other for the Negative half wave.
    Is that how it works, just interested to know!

    Yes, I see what your saying with current limiting & also working with not enough good equipment to do the job properly, it makes things hard & a real headache.

    Yes, of course the project is about controlling the Universal motors, I just thought that if I can control something small on the bench first & get all my set point circuits made properly & everything operating as it should I can then setup the Universal Motor control easily.
    This would allow me to have a relatively relaxing time with minimal noise & excitement so to speak, as you know the universal motors are full of noise & vibration.
    At the moment I am still inside at my work table & something small & quiet would be good to learn from.

    What do you think?

    Cheers
     
    Last edited: Jan 17, 2016
  12. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I don't like your idea at all. Braking s NOT a way to control speed.I did a tension controller once, but I did not implement reverse voltage which makes the clutch less effective. It turned out we did not need it.


    The one I came up with is to use a hair dryer.
    1. They are inexpensive
    2. Don't use heating

    1. You could use pressure
    or

    2. use a resistor where you apply some voltage too, to make it slightly warm. Attach a fast response thermister to it and try to control it's temperature by cooling. It does make it a reverse-acting controller. Higher T, less fan.

    2. The light bulb might work too, but instead of controlling the bulb, control the amount of forced air cooling from a hair dryer operating in "cool mode".
     
  13. willeng

    willeng Member

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    Hi Kiss,
    I see what your saying & have edited my above post.

    Ok, I will see what I can do with controlling something.
    We don't have a hair dryer as we are pretty much old school.

    You have given me some idea's!

    Cheers
     
  14. willeng

    willeng Member

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    I still have the resistor across the traic output, it was 2.3K but I adjusted it to 3K now things are working correctly, this gets warm so I could control it's temperature with air cooling.
    It has good insulation around the outside so should not be a problem.

    Would that be Ok?
    Cheers
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    True. The Littlefuse note has a circuit.

    One comment I remember from yesteryear was that both SCR's could be fired simultaneously to damp transients. But, I don't know how that works.

    I'm not even sure how the current limiting worked.
     
  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    You just might have to find a surface mount thermistor.

    I just thought hair dryers are cheap and possibly found at a thrift store.
     
  17. willeng

    willeng Member

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    Hi Kiss,
    Sorry I have been reading previous posts about the Voltage Reference to the Aref pin on the Arduino.
    I had a severe mental blank about this, which is not unusual but what I wanted to know is:

    Can I use a 2.5V reference if my maximum voltage input to the Arduino is going to be 5V, basically, can a reference voltage be lower than the maximum input if it is a good stable reference voltage.

    Cheers
     
    Last edited: Jan 17, 2016
  18. willeng

    willeng Member

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    I found some LM336-2.5 Reference Diodes.
    It seems from the datasheet that if LM336 is used with a LM317 the reference voltage can be adjusted higher than the 2.5V if that is not suitable.
    Could you have a look at the datasheet for me & suggest which circuit would be best, I was thinking that (Figure 2, page 5) or the circuit using the (LM317, page 6) would be good?

    Cheers
     

    Attached Files:

    Last edited: Jan 17, 2016
  19. willeng

    willeng Member

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    Hi Kiss,
    Sorry, forgot to comment on the Blower-AKA hair dryer, I actually thought that it was a good idea & you can get them cheaply as my wife has said.
    My wife has offered up her Vacuum Cleaner under the conditions that if I blow it up she gets a new one haha!

    I have decided to use the vacuum cleaner as it is of course a universal motor, I can connect a manometer onto it & use the MPX2010DP sensor as will be used in the final setup.
    The noise is not to bad with the motor being enclosed so it should be good to go.
    It has a variable speed pot so I will just bypass that, it should be good to test the PID out.

    I would still like to know about if the reference voltage can be lower than the maximum input voltage, I have done a fair bit of reading & some say the reference voltage basically can be say 2.5V & the input can be higher & others say the reference voltage should be the same as the highest input voltage so I am still unsure about this.
    I have read that the Arduino Mega 2560 like I have has internal reference voltages of 1.1V or 2.56V so if the 2.56V can be set & used this would be good?

    Cheers
     
  20. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    This https://www.arduino.cc/en/Reference/AnalogReference pretty much covers it.

    The reference should closely match the anticipated max sensor output. The only reason is to get the most resolution. If you expect 0.7 out, then a 5V reference doesn't make sense. i.e. 1/256 of 1.2 (reference) is better than 1/256 of a 2.5 V reference for a 0.7 V max sensor.

    The reference voltage can only be up to the processor power supply. Some of the new Arduinos are 3.3 V.

    The pressure sensor isn't your typical automotive sensor. It basically requires an instrumentation amp. If you really wanted to calibrate it,you need to compensate for a small offset. There are some single supply zero offset IA's that we'd have to select. Generally the importance is to drive the output reference of the IA with a low Z source.

    In an automotive environment they use sensors that are called "ratiometric" They are powered from 5V and the reference to the A/D might be 1/2 Vcc. That means whatever Vcc is. It could be 5.1, 5.3, 4.9 or whatever. So, the reference tracks the instantaneous output of the power supply.

    See http://www.analog.com/media/en/technical-documentation/data-sheets/AD8237.pdf Pay particular attention to PDF page 21.
     
  21. willeng

    willeng Member

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    Hi Kiss,
    Thanks for that, I will have to look at the links you supplied properly.

    I have an INA126P Instrument Amplifier that I have setup & Calibrated so 100mV = 1" of Water, 40" Water maximum = 4V output.
    It works pretty good.

    I setup the Vacuum Cleaner with a manometer etc, bypassed the circuit going to the universal motor & connected everything up ready to go.

    I am ready to test a few things out, get back you when I see whats happening.

    Cheers
     

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