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Thread: The big TEC driver thread!

  1. #151
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    Quote Originally Posted by dnar View Post
    I have added setting the set point (in degrees Celcius) to the EEPROM. The valid range is 18-26C in 1 degree steps. If an invalid value is detected, the default of 22C will be used. If anyone thinks this range should be larger, state you case.
    Since you're creating this posibility to set the Temp. would it posible to do this in 1/10 deg. and as user changable values have 180-260. Code internal Value/10?

    cheers!

  2. #152
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    Quote Originally Posted by Solarfire View Post
    Since you're creating this posibility to set the Temp. would it posible to do this in 1/10 deg. and as user changable values have 180-260. Code internal Value/10?

    cheers!
    While that would be possible, why would you want to set to the decimal place? Just trying to understand the need.

    It is not that easy with 0.080924 degrees C per ADV value.
    Last edited by dnar; 01-25-2011 at 23:01.
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  3. #153
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    I have a special version of code vision somewhere. I'll email it thru Wayne :-)


    Quote Originally Posted by dnar View Post
    I have added setting the set point (in degrees Celcius) to the EEPROM. The valid range is 18-26C in 1 degree steps. If an invalid value is detected, the default of 22C will be used. If anyone thinks this range should be larger, state you case.

    I also converted the code to WinAVR/AVR Studio as the code now exceeds the CodeVisionAVR evaluation size limit. I prefer WinAVR personally.

    AVR Memory Usage
    ----------------
    Device: attiny13

    Program: 410 bytes (40.0% Full)
    (.text + .data + .bootloader)

    Data: 15 bytes (23.4% Full)
    (.data + .bss + .noinit)


    Build succeeded with 0 Warnings...

    I'll post the hex file up once I have tested, it compiles but I have other things to do today like get the Barbecue cranking and get drunk! (Australia Day Holiday).
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  4. #154
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    Quote Originally Posted by dave View Post
    I have a special version of code vision somewhere. I'll email it thru Wayne :-)
    It's Ok Dave, I prefer not to use it. I prefer the WinAVR libraries, and all my other projects are in WinAVR/GCC.
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  5. #155
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    Quote Originally Posted by dnar View Post
    While that would be possible, why would you want to set to the decimal place? Just trying to understand the need.

    It is not that easy with 0.080924 degrees C per ADV value.
    The main thought behind this is too maximize the flexibility of the set point. As far as the PI control is concerned it really doesn’t make a big difference if the set point X = 22° or 22.4°. Just trying to use the max on flexibility that this controller has to offer in its current state.


    Also it would make it easier to hit the sweet spot of a diode or influence mode shifting.


    Actually the same effect could probably be achieved by simply adding a VR of about 1-10k in series to the NTC.

  6. #156
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    Quote Originally Posted by Solarfire View Post
    The main thought behind this is too maximize the flexibility of the set point. As far as the PI control is concerned it really doesn’t make a big difference if the set point X = 22° or 22.4°. Just trying to use the max on flexibility that this controller has to offer in its current state.


    Also it would make it easier to hit the sweet spot of a diode or influence mode shifting.


    Actually the same effect could probably be achieved by simply adding a VR of about 1-10k in series to the NTC.
    Understood. Due to the rough nature of the analog input and ADC, you don't have precise 0.1c increments. In fact each 1c I am providing are not all spot on XX.0. But, close and with good stability/accuracy.
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  7. #157
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    Default Mikes TEC kit

    Just got mine today.

    Advance technical discussion??
    I'll say- WAY over my pointy lil head- but I will try.

    hak

  8. #158
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    OK.. here’s an update on the redesigning status of the beer keg cooler control.

    Got 3 versions at this point. All are realized with CADSoft’s EAGLE V5.11 (http://www.cadsoft.de/download.htm) of which the freeware version is more than sufficient for editing and manufacturing of this PCB. Most PCB-Manufacturers will accept the EAGLE PCB *.brd file for manufacturing the PCB. Circuit portions were tested with NI Multisim. Layouts will be posted later.

    A non SMD, single layer version of the original circuit except for the HEXFET which is mounted on the solder side. I couldn’t find a better substitute and since all pins on one side of the chip and three on the other side are all connected with another it shouldn’t be a problem for anyone to solder.
    A non SMD version with all of the mentioned below except no H-Bridge.
    A non SMD version with all of the mentioned below except with H-Bridge (heating/cooling).

    On the list for a new design are:
    1.)Precision op-amp NTC front-end to optimize the ADC range with a small window.
    Setup for a temperature range from 27°C-10°C (120mV-4300mV) giving ~ 51ADC inc./°C.
    2.)Dedicated ADC Voltage Reference.
    Used a precision low drop voltage regulator LP2950 tight initial
    Tolerance (.5% typ.), extremely good load and line regulation
    (.05% typ.) and a very low output voltage temperature coefficient, making the part useful as a low-power voltage reference.
    3.)Output inductor LPF to produce true analog output for the TEC.
    Still needs to be determined, depends on the PWM freq. of the Attiny13 output.
    Wayne, I need to know the PWM frequency of the output.
    4.)Re-assignment of ATtiny13 I/O pins (TEC output on port B0).
    Reassigned most pins (see schematic). Wayne can you take a look at this and say if these assignments are OK?
    5.)Possible change to another MCU, ATmega8 for example to provide adjustable set point trim pot.
    Pending
    6.)Mounting holes on the PCB.
    Done
    7.)Screw terminals for power, TEC, fan and sensor.
    Done
    8.)Possibly current limiting also.
    A little tougher with an H-Bridge implemented.
    Possibly do via the PWM output using PB5 (Reset) as an analog in for reading a set point via trim pot setting 0-5V. Hey Wayne, is this power up Reset circuit necessary? Some reading I’ve done says no? If we could use this input for current limiting.
    9.)Possibly a trough-hole PCB to aid hand assembly.
    Done
    10.)Analog monitoring output to read in either 100mV/C or 100mV/F.
    Pending
    11.)Standard 0.1" pitch 6-pin in circuit programmer connector. OK
    Done
    12.)Diode driver inhibit output if the temperature is outside of a predefined window.
    Software out on PB2
    Attached Thumbnails Attached Thumbnails TEC Controller no SMD 60W.pdf  

    TEC Controller no SMD 30W.pdf  

    TEC Controller no SMD 60W Basic.pdf  


  9. #159
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    Quote Originally Posted by Solarfire View Post
    If we could use this input for current limiting.
    Is a AVR going to be fast enough to do this? The fastest (best?) way would be to use the tiny 13's comparator to trigger a interrupt right? I guess that would be fast enough, but that would need 2 extra input pins.
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  10. #160
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    Quote Originally Posted by dave View Post
    Is a AVR going to be fast enough to do this? The fastest (best?) way would be to use the tiny 13's comparator to trigger a interrupt right? I guess that would be fast enough, but that would need 2 extra input pins.
    Actually the thougt was a little more simple. A ref. voltage of 0-5V on an input (PB5) determins/limits the max % PWM after the PI(D) loop on the output. For example, since the H-Bridge outputs 3A at 100% PWM the 50% should = 1.5A. I don't think anything more would be neccesary.
    Last edited by Solarfire; 02-06-2011 at 04:42.

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