Any advice for a DIY control system

[stegoodall]

Hi
I am making a system that controls power to plug sockets for my A level computing project, I was wondering if anyone had any advice on how I could make it so it turns a socket (for fans) on when a certain temperature is reached (i.e. a DIY temperature probe), The probe must be able to plug in a PC, also the ability to create a graph or something would be good. Any advice? Also a similar idea with pH, controlling solenoids maybe, would be good but I don't know how hard that would be.

Cheers
Stephen

[pavlo]

The simplest way is to use a PIC microcontroller, such as a pic16f628 you have up to 16 inputs or outputs. you can read a temperature sensor (thermistor) using an analogue to digital converter which can be connected to the pic or you could use the thermistor as part of an RC circuit and let the PIC time how long the circuit takes to charge the capacitor, this is much simpler to build but involves more programming.

The PIC can easily be programmed to give serial data output compatible with an rs232 interface on a pc or lcd display (or both).

The plug sockets can be switched using a relay. The output from the PIC will need to be buffered by a transistor to avoid overload (each pin on the pic can sink or source about 25ma).

Hope this gives you a few ideas. If you need any help, please get in touch

Cheers

Paul

[stegoodall]

I am planning on using a "usb experiment board" which has 8 outputs and I am also planning on using DPDT relays to control the power. Are thermistors waterproof?

[sid8ball]

If your using a usb experimental board, you need analogue inputs to measure ph, temp etc. you will need separate circuits for temp, ph to convert the signals to a measurable voltage for the analogue inputs. You can find sealed thermistors for liquid measurement. The relays will indeed need the digital outputs to control them (signals required can range from 1 to 15V) and normally a separate power supply as well.

[stegoodall]

I was planning on a 12v supply (probably a variable one - the big black plugs) for the relays. Does anybody know if the PIC's can be programmed in Delphi, and would it cost a lot to use them and the converters etc that pavlo mentioned?

[sid8ball]

I was planning on a 12v supply (probably a variable one - the big black plugs) for the relays. Does anybody know if the PIC's can be programmed in Delphi, and would it cost a lot to use them and the converters etc that pavlo mentioned?

pics have a basic programing language making them very easy to use. This would be the cheapest option to use. If you have a google you wil probably find an example of what you are trying to achieve.

[stegoodall]

I've just had a quick look at your program and it looks similar to what I am trying to make, but a lot more advanced. Would I be OK to pm you for advice when I have decided what I want the program to do?

Edit: Just thought I would add, I aren't deliberately copying you, I asked someone on this forum if they would be my guinea pig in June :D but with the summer holidays I haven't started yet lol:rolleyes:

[sid8ball]

no worries, Ill help you all i can.