Thermistor into XP computer excel

My experience has been that the game port is sloppy at best. I don't know what kind of accuracy you want but I don't think you can expect much from the game port. I'd imagine there are many A>D boards (eBay?) to pick from which could handle the thermistors for you.

Sounds like a perfect application for a microcontroller. Quite a few include 8 A/D ports that could easily read the drop across a thermistor, do some digital filtering, and send the result out to a PC via a built-in UART.

Is this something a keen DIYer could handle?

Rob

Absolutely. You could do it with, for example, one of Atmel's STK-500 "starter kits" (about $80 from Digikey) and a handful of thermistors plus resistors for the "other half" of the voltage dividers. The STK already has the RS-232 level shifters and a DB-9 connector that can go to the PC. You'd need to setup the A/D channels, the UART, and a timer plus the usual glue code. All pretty easy to do with assembler, following the examples in the product datasheet.

They used to include (IIRC) an AT90S8515 with the STK. Not sure which one they include with it nowadays.

An ATmega8535 would be good for this application. It's available in a

The only "gotcha" with these is that the ATmega(series) usually ship with the system clock set to the internal oscillator. It's simply a matter of using the programming software (free from Atmel) to set a fuse to tell it to use an external oscillator or crystal but it's possible to forget to do that.

An alternate route would be something like the PMD-1208LS from Measurement Computing. The total cost is in the same range.

spreadsheet.

What you need is called a Data Acquisition Card. It plugs into your PC's Expansion Bus.

"rob" schreef in bericht news: snipped-for-privacy@posting.google.com...

Rob,

You can expand to four channels as a game port contains two sets joystick connections. But without extra electronics that's the limit. You can look for analog multiplexers to serve more thermistors but to control them you need some output from the computer. The game port has no outputs so you'll need the serial - or parallel port for it. When you come so far you can as well go all the way and use the serial port to do whole the job. A PIC or AVR micro with build in AD convertors and a UART will perform much better then a game port both in reliability and accuracy. You sure will have to invest in some hardware and have a learning curve but IMHO the alternative will take the same cost with worse results.

petrus bitbyter

Rich,

Is the programming software an assembler, a compiler for a well-known high level language like C, or what? In what hardware/software environment does the software run, and how do you get the machine code over to the chip?

Just trying to get my feet on the ground...

TIA

Ed

This would be pretty quick in assembly, assuming that you did the heavy lifting of converting from sensed thermistor voltage -> resistance ->

temperature over on the PC side; that is, send the A/D result over to the PC. All of the conversion could be done in assembly, of course; doesn't seem to be a good investment of time when it's simpler on the PC side.

C would work as well, of course. There is a cross-compiler, gcc port (i.e., free GPL software) available for the AVR family. For downloads (of this and other goodies) as well as app notes and general info, click over to

There is a range of commercial C compilers, as well. I use ICC-AVR from ImageCraft

As far as loading the assembled or compiled code, most AVR device programmers accept Intel-hex input files. There is a free assembler / debugger / programmer-driver package, "AVR Studio 4," available from Atmel at

I'm beginning to get the picture. You work on the PC using a development environment, finishing up with generation of a file of hex codes. That is downloaded to the microcontroller currently plugged into the STK-500. Then you move that chip to a project board with the ancillary electronics to make it all work?

TIA

Ed

Correct. Alternately, you can use the STK-500 to do in-system programming to a chip on a project board (or soldered to a PCB) by connecting a ribbon cable between the STK-500 and the target system. The manual

For your app -- A/D converters to the outside, serial port to a PC -- everything could be done on the STK-500 without needing a separate board. So if you're just monitoring, say, the home thermostat over a

Dataq has a 4 channel, 10-bit A/D converter that connects to a serial port for $24.95US

It's probably the cheapest intro kit available - and includes software!

John