TEC controller

[pedja089]

Why not add another sensor on hot side of TEC to control fans independently from TEC?

[NickMu]

Hi Pedja089,

This might be one of the improvements that I thought about too, in case this first minimal approach will not work.
I’m also planning on adding a temperature sensor / thermostat on the cold side (if my testing finds it necessary) to prevent freezing of the TEC. I have some trusty DS1821 that can be programmed for different trigger temperatures.
I wanted to start simple which is the reason why I’m using the same output for fans and TEC for now.
The nice part is that the cooler is back together, I have access to all wiring and I can do all the work /changes externally.

Thank you for interest and support.

Nick

[NickMu]

This is the latest addition to the TEC controller: One pot on ADC1 sets the temperature.
I’ve done it such way so with a linear pot the target temperature can be set between 40 and 65 degrees F.

'Last release 9_16_16 Implements pot for setting set_temp
@__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
pwm_flag        var     bit

start_ch        con     126
end_sym         con     251
samples         con     39 
divider         con     20
hysteresis      con     1
min_pwm         con     30
max_pwm         con     50
full_pwm        con     40

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=69
        id="1"
        pwm_flag=0
        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
        return
read_set_temp:
        new = 0
        For temp_index = 1 TO 9
        ADCIN 1,adval
        new = new + adval
        Next
        set_temp= 40 + new/100  'keeps set_temp between 40 and 65 deg. F
        return

decide:
        If act_temp < (set_temp-hysteresis) then 
        pwm_pars =0
        pwm_flag=1
        endif
        If act_temp > set_temp and pwm_flag =0 then 
        pwm_pars = min_pwm+(act_temp - set_temp)
        goto jump
        endif  
        If act_temp > (set_temp + hysteresis) and pwm_flag =1 then
        pwm_pars = start_pwm
        pwm_flag=0
        endif
jump:
        gosub set_pwm_pars
        val_1=act_temp
        val_2=pwm_pars
        val_3=set_temp
        Return
Main:
        gosub read_act_temp
        gosub read_set_temp
        gosub decide
        gosub send_out
        pause 1500 
        goto Main    
end

I think that I will settle for that now. I will just test its performance for the next week or so and wrap the project up for this particular cooler.
A friend of mine is offering me a huge 125 bottles cooler with refrigeration problems (old Freon compressor type). If this first attempt will prove successful I will spend more time saving the big cooler which is a lot nicer and a lot more expencie than this one.
I manage to get 6 brand new TECs, more powerful than the other ones (7-8 Amps) and I will start experimenting with them and different setups.
It might take a little time but I will keep you posted.

Thank you everyone for the input.

Nick