IceX

Hi Guys,

Let me start of:

I am a total newbie, I have build like 1 kit 8channel remote relay with instructions given, they said is was not for beginners, but with instructions what is?

I don't understand a lot from the hardware side of things (software = ok I am developer).

I want to basically know:
I need to build a temperature switch (very cheap), that will:

1. Allow me to set the on / off temperatures.
2. I need to set the min temp to turn on the device.
3. I need to set the max temp to switch off the device.

I need to please have someone explain me on how to design this. I have done almost research for 7 days now and did not find anything (expect for someone selling something similar):


The problem is this device is for only heater or cooler, cannot control both at same time and their rated amps are very low...

I am looking for circuit diagrams for such a project. To give more details behind this.

The input voltage = 12V dc rated 1.3amps

I need the switch / relay to close (powering the device) when the device is between the min / max temp and to open (stop power) when the device is below the min or above the max.

I need the exact same 12V dc rated 1.3amps output.

Reason:
This is to turn on an LCD screen (in my car - carputer), but I can only do this in the min / max range. Sometimes the car stands in the sun and it takes about 2 minutes for car to cool down with airflow ect.

This will avoid the LCD from obtaining damage due to being turned on while to hot or too cold.

I have fans and everything hooked up, but only want to switch power to LCD if this is in the operating temp as indicated by manufacturer of LCD.

Thank you (and please remember I am a total newbie)...

I need to know which parts to buy and how they will fit into the circuit diagram, I have pcb board, I have soldering station, I have all the toys, just not the know how.

specie

1 Do you want to display the temperature?
2 Are u interested in microcontroller based design?
3 Do you want variable set points?

IceX

1 No it will be concealed behind LCD (so will not be visible).
2 No (but it would be nice): this might add value as if I can get it to work with USB ... I can then display the temperature on LCD by reading it from board (but this is really not a must, I will do this if I can otherwise will accept without microcontrollers)?
3 Yes (by default the temp can tollerate -20C to 70C so I have read, but I have problem with LCD display from +50C, the min can be fixed set to 0, and only the max adjustable, but would be better if both can be set.

(If it is possible to put in a USB for reading: I might as well use it to write the min / max using USB to the controller - I will program the software to do this)

Thanks...

IceX

Anyone out there have this kind of diagram or details for me?

ericgibbs

hi,
As you dont need to display the actual temperature and the min/max switching levels will be fixed, I would suggest a LM35 temperature sensor ic and a LM393 dual comparator.

The two halfs of the dual LM393 could be used for minimum Cdeg and maximum Cdeg. The LM393 outputs would drive a transistor which in turn operate relays.

It could all work from the cars supply.

Does this help..?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

IceX

Not really... the reason being is that I am totally new to hardware. I have sort of an idea and have read some other diagrams and understand how they work and why, but not at the stage where I can design my own (which I would love to be at)...

I have tried accessing some resources (from the site, and googled and other sites) and would really love to start learning the hardware building of pcb boards and components seriously, but seem to not find any open source articles or good ebooks or learning resources...

I assume with this I would need:

1. 12V DC Relay to switch
2. 2 V transistors?
3. Maybe a fuse (for surge protection if amp rating goes over 1.3amp, but should not really)?
4. LM393 (I don't know how this chip looks like) < and don't know what hardware I would need to program it using c (microprocessors) < I can do the coding but not sure how to write to chip (e-prom writer?). Are there different sizes?

Excuse my question but I am totaly newby to this

ericgibbs

hi,
The LM393 is not a PIC, so there is no programming required.

You would require a relay/s, a couple of transistors, a few other components as well as the LM393.
The LM35 tempr sensor component is not very expensive and can work over the -50Cdeg to +150Cdeg range.

I cant think of a simpler and cheaper way of doing with electronic components,

Are you able to use a soldering iron.?

Where are you located.?

EDIT: exactly what tempr do you want the relay to operate.??

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

IceX

I understand what you mean, however, the temperatures you give seems extreme... if it really gets above 150 in my car... the interior would start melting ...

The LCD can operate well from -10Cdeg to 45CDeg (I took 5 of from max, because it will operate at 50, but screen showing blury, above 50 screen is white with black stripes, below 45 it seems to operate good).

Hope this helps, I could maybe even fix this on the diagram on board... and not make it adjustable...

Which should make the switch easier to make.

The fans run on ignition, thus it will always operate when the key is turned on which is fine, but the LCD should only be turned on when under 45Cdeg.

ericgibbs

Hi,
Look thru electronic suppliers catalogues, you will find simple thermal switches that operate at fixed temperatures. Various temperatures are available.

I'll look thru my data and try to post an image of these devices, they are not expensive.

EDIT:
This is the type:
http://cpc.farnell.com/jsp/search/re...isGoback=false

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/