TEC controller

[NickMu]

Just a quick update: I’ve tried all three suggested methods and they all work as expected.
I will do some more hardware changes, now that I have a stable test code. I will experiment especially with frequency changes and inductors values. I’m trying to get as much efficiency as possible.
What is encouraging though is that running the prototype for long time does not generate heat at all. The main power components are cold and the current draw (from the 12V source) swings between 1A and 2.5A.
I will post the latest working code as soon as I get it cleaned up.

Nick

[NickMu]

This is the working code. It steps up through 21 steps of PWM (from 30 to 50) and then steps down (from 50 to 20). The result is an output voltage between 5.5V and 8.5V (the numbers are rounded up). This is design for testing the flexibility of the system only. Final code will implement a temperature controlling algorithm. BTW I switched to PIC16F819 since this is the PIC I'm going to use for this task.

Code based on Dave's input (183):

@__config_device_pic16f819
@__config_wdt_off
@__config_hs_osc
@__config_pwrt_on
@__config_mclr_off
@__config_lvp_off
@__config_protect_on
@__config_CCP1_RB2

OSCCON=%01110111     
DEFINE OSC 8        
            
i           var         word
pwm_out     var         PORTB.2
pwm_pars    var         word
min_pwm     con         30
max_pwm     con         50
CCP1CON = %00001100     
PR2 = 15            
CCPR1L = 0         
CCP1CON.5 = 0
CCP1CON.4 =0
                                                                                               
    High pwm_out
    Pause 500
    Low pwm_out
    T2CON.2 = 1 
    goto Main
set_pwm_pars:
     CCPR1L = pwm_pars >> 2
     CCP1CON=$0C|((pwm_pars&$3)<<4) 
     RETURN
Main:
     for i=min_pwm to max_pwm
     pwm_pars = i
     gosub set_pwm_pars
     pause 250
     next
     for i=max_pwm to min_pwm step -1
     pwm_pars = i
     gosub set_pwm_pars
     pause 250
     next
     Pause 5000
Goto Main

With the same main loop I changed the subroutine set_pwm_pars based on Pedja089 input (163):

set_pwm_pars:
     CCP1CON.5 = pwm_pars.1                
     CCP1CON.4 = pwm_pars.0
     CCPR1L = pwm_pars >> 2
     RETURN

Finally my simplified version for the subroutine (187):

set_pwm_pars:
     CCP1CON.5 = pwm_pars.1                
     CCP1CON.4 = pwm_pars.0
     CCPR1L = pwm_pars / 4
     RETURN

The output from all is the same (as expected). Cannot comment on execution speed and for my purposes it doesn’t really matter. I will only set a step, based on the temperature control algorithm, and sit on it for a while. I’m sure that the wine will not mind a few microseconds shifted response.
The one difference between the three versions is the code space required. The numbers in parentheses are showing that.

So far I’m happy with my results.
I will work on the hardware for the next few days and start working on the temperature control algorithm after that.
Before I start this new task I’m asking all the people in this forum that might have some experience in this field: Am I on the right track? Is there a better way to do it?
I love its simplicity and the fact that I fully understand how it works but in the same time I hate to find it out that is wrong after I already spent a lot of time on it.

As always looking forward for input.

Nick

[Dave]

The only problem I can see is that you are assuming the other bits in the CCP1CON are always set correctly? For the sacrifice of a few extra instructions I would prefer to have ALL register bits set as in: CCP1CON=$0C|((pwm_pars&$3)<<4)

[NickMu]

Hi Dave,

You are making a good point. It comes with lock of experience on my side.
As I said before I have two good qualities: learning extremely slow and, in contrast, forgetting extremely fast.
At this point I’m not looking to save program space so I guess playing safe will be a good idea.
Any input on the hardware side?

Nick

[NickMu]

I got all the hardware working and wrote a simple temperature control program. Nothing fancy.
The code drives the TEC with different power output levels depending on how far the real temperature is from the set temperature.
I don’t have yet a mechanism of setting the target temperature but this is just to prove that the system works.
Since the major hardware is in place and the cooler is basically functional I will settle for now for a fixed, preprogrammed target temperature.
The ICSP connector for the 16F819 is accessible and I will play with the code to get more features.
I’m forced to take a break from the project but I will get back to it when time permits.
For now 62⁰F should be fine on most of the wines I drink so I’ll make it default.
Anyway it has been a fun weekend project and what makes it special is the fact that I did not have to order any parts. Recycling old junk makes me feel really good.
For all interested below is the simple control code, not fully tested since I just finished it last night. There are few things in the code that are not fully implemented (serial output will be used for a LCD display, hysteresis, id (to diferenciate between the two chambers). These variables will be used for future development when time comes.

@__config_device_pic16f819
@__config_wdt_off
@__config_hs_osc
@__config_pwrt_on
@__config_mclr_off
@__config_lvp_off
@__config_protect_on

DEFINE OSC 8        

DEFINE DEBUG_REG PORTB
DEFINE DEBUGIN_REG PORTB
DEFINE DEBUG_BIT 6
DEFINE DEBUGIN_BIT 7
DEFINE DEBUG_MODE 1                
DEFINE DEBUG_BAUD 38400

DEFINE  ADC_BITS        8
DEFINE  ADC_CLOCK       3
DEFINE  ADC_SAMPLEUS    50
ADCON1=%01001110  

pwm_out         var     PORTB.2

adval           var     word
val_1           var     byte
val_2           var     byte
val_3           var     byte
new             var     word
act_temp        var     byte
set_temp        var     byte
new_temp        var     byte
temp_index      var     byte
i               var     word
pwm_pars        var     word
id		var	byte

start_ch        con     126
end_sym         con     251
samples         con     39 
divider         con     20
hysteresis      con     2
min_pwm         con     30
max_pwm         con     50

CCP1CON = %00001100     
PR2 = 15            
CCPR1L = 0         
CCP1CON.5 = 0
CCP1CON.4 =0
                                                                                               
        High pwm_out
        Pause 500
        Low pwm_out
        T2CON.2 = 1
        set_temp=62
        goto main     

send_out:
        debug start_ch,id,val_1,val_2,val_3,end_sym
        return 

set_pwm_pars:
        CCPR1L = pwm_pars >> 2
        CCP1CON=$0C|((pwm_pars&$3)<<4) 
        return

read_act_temp:
        new = 0
        For temp_index = 1 TO samples
        ADCIN 0,adval
        new = new + adval
        Next
        act_temp=new/divider
        If act_temp <= set_temp then 
        pwm_pars = 0
        else
        pwm_pars = min_pwm+(act_temp - set_temp)
        if pwm_pars>max_pwm then pwm_pars=max_pwm
        endif
        gosub set_pwm_pars
        val_1=act_temp
        val_2=pwm_pars
        val_3=set_temp
        Return

Main:
        gosub read_act_temp
        gosub send_out
        pause 1500 
        goto Main    
end

Regards,

Nick

[Dave]

Nick, The statement:

if pwm_pars>max_pwm then pwm_pars=max_pwm
endif

can be made as such: pwm_pars = pwm_pars min max_pwm

That way no if then is needed.

[NickMu]

Hi David,

Thank you for the hint. It will be first on my “To do” list.
I noticed it in your first post and mark it as a good candidate for the time when I will do code optimization. I just slapped the code together to see how the system works in a dynamic scenario and prove the concept. The way I thought it is that when the actual temperature is way higher than set temperature the system will push maximum power. The closer the two temperatures are the system reduces its output. Only when the actual temperature is lower than set temperature the TEC will be turned OFF. This reduces the number of ON / OFF cycles which I understand the TECs are not happy with.
I am open to any other suggestions that will improve the project.

Nick