Please help with code for DS18B20

[lew247]

Sorry Alain, I wasn't too clear on what I meant.

The easypic board HAS pullup resistors on those ports.

When i run the program, the lcd sits there with just the * displaying even when no button has been pressed (portA.0 in this circuit/program)

it does nothing else.

When I press portA.0 the display cycles through set temp (which I can set properly with portA.1 and portA.2)
Next press brings it to the Hysteresis which again will set ptoperly

the 3rd press brings up the temperature display mode (mode 0 )

It displays the temperature at the moment the button is pressed but it never updates or checks again.

I have checked it works by holding down the button on portA.0 and if held down (LOW) then the display works properly, measuring the temperature continious, and if the temp changes it makes port C.0 or C.2 high depending on the set temp and hysteresis.

My problem is I cannot get it to continually measure temperatre without holding down portA.0

Also when I turn the power on first all I get is the LCD blank other than * being displayed.

Having read the code, * should only display after each button press, but it always displays.

Also I'd like it when power is turned on to measure and show the temperature continoiusly until the button (portA.0) is pressed.


Hope that made more sense, as I knew I couldn't put resistors inside the pic

[malc-c]

Very informative thread and funny enough something that I was hoping to work on myself as I'm looking at replacing the simple on/off thermostats that control the heating in my reptiles vivariums.

Can someone (Alain?) post up a schematic for the project. (or settings for the EasyPIC5) - I'm looking at trying to develop this a bit further so the output is pulsed, with the mark / space ratio reducing as the set point is neared. I've used commercial on/off stats, and the temperatures are hard to control. The idea is to keep the hot spot fairly constant and below 35C max, as constant exposure to a surface above this temperature can cause a burn risk to snakes.


With the thermometer probe placed on the shelf near the logger (it wasn't actually touching the same spot), and with the thermostats sensor in the cool part of the shelf, the thermostat was set so the digital thermometer read a max of 34C. Here's are the results - the bit you are interested in is between 18:00 hrs onwards



Obviously the heat was conducting through the wood, which cooled slower than if the sensor was measuring air or the surface of the heater. But you can see that there is a large temperature swing between the min and max readings, and that the surface reached over 40C

To reduce this difference I placed the two probes next to the logger directly above the heater. Here is the results, which still show the same cycling, but with a lower differential (average 5 degree C), but is more stable



The pulse proportional stat reduces the cycling as it's not switching the heater on/off/on, it maintains a steady temperature by pulsing power to it thus the heater never cools.

I could purchase a couple of commercial PP stats for around £100 (possibly less via mail order) but then where's the fun in that Now I know there are a lot of you experience programmers that have dabbled with PWM, so wonder if you would like to add your comments here.

[malc-c]

In the set up below I used a commercial data logger to record the surface temp of the shelf over a 24 hr period.



Although I had originally posted this in my post above, the forum software said I had more than 4 images ????

[Darrel Taylor]

Malcolm,

Sounds like the perfect job for a PID loop.
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[Acetronics2]

Hi, Malc

Do you understand the "why" of the Parallax document, now ... ???

You'll have to place your Button Key INSIDE the vivarium ( hé,hé ... WITH the snakes !!! ) if you want a true image of your temp.

The graphs you've shown can't be used to finely trim a regulator ... but are a good example.

Temp measurement and moreover probes placing is a real art ... to get a nice temp regulation.

But let's begin by the beginning :

ALL you have to do already is in ZE Book ... with relevant code.

We'll see details later ...

Till then, I'll implement the PID Regulator on my existing " 84 " Thermostat ( not the one shown here, but a nicer one which is pin for pin compatible !! )

Alain

[lew247]

Alain

You were right as always. I hadn't the board configured properly.

I totally forgot about the row of jumpers to set the pins pull-up or pull-down, I had it set wrong.

Thank you

[malc-c]

Hi, Malc

You'll have to place your Button Key INSIDE the vivarium ( hé,hé ... WITH the snakes !!! ) if you want a true image of your temp.

Alain

Agreed,

I've just taken a further reading with the probes 2" from the heater, so its sampling the air temperature. Here's the result (the button logger still on the shelf as shown)



If you ignore the fluctuations in between 10pm and 3am when the snake was out and obviously laying on the sensor, and look at the period 4am to 4pm you'll see it a lot more stable and only has a 0.2C deviation.

DT, could you elaborate on a PID loop.

Alain, could you provide a link to that file... I'm frantically searching for a DS1820 so I can start developing this project, but as my PBP programming is so rusty (and basic) may need you guys to offer some assistance if I get stuck (or should that be when I get stuck )

[malc-c]

DT, could you elaborate on a PID loop.

OK - google was my friend

http://en.wikipedia.org/wiki/PID_controller

[Acetronics2]

Sorry Alain, I wasn't too clear on what I meant.

The easypic board HAS pullup resistors on those ports.

...

Hope that made more sense, as I knew I couldn't put resistors inside the pic

Hi, Lew

You have a HARDWARE misconfig somwhere on your board ...

the program AT THE MOMENT, is running aboard my EasyPic5 ...

Check pullup jumpers on Porta.0,1,and 2 : UP
check buttons jumper : GND

Nothing more nothing less ...

Alain