K8055 Programming help

Kits PC Related Projects
1

Hello everyone,
I have limited programmign skills and need some help (in fact I’d be willing to pay for what I need)

What I want to do is use this board to control 2 x 0-5v control voltages and then in turn read 2 x 0-5 v control voltages.

Basically what i have are 2 flow rate controllers that I want to control, these flow meters are controlled by a zero to five volt signal that I’d liek to coem from the K8055, the same flow meters then report back the exact flow in a zero to five volt signal.

I’d like a program that will also conduct soem calcualtions. Basically I’m mixing concnetrations of gas with 2 flow meters and I want the program to ask for the required concentration work out what flow rates are needed set the volatges and then report the result as a concentration (the maths is easy)

If anyoen can help please contact me ASAP

Coulson_ian@hotmail.com

2

Notice that the two analog outputs aren’t very powerfull, maybe you could hook the sensors up to the USB’s 5V directly?

And what should the program be written in? In what format do you want the output from the sensors?

3

[quote]Notice that the two analog outputs aren’t very powerfull[/quote]At the analog outputs of the K8055 there are 1k5 series resistors as short circuit protection.

[quote]Basically what i have are 2 flow rate controllers that I want to control, [/quote]Do you know the input current consumption or the input resistance of these flow rate controllers?

4

Thanks for the messages and please accept my apologies for my late reply ( i had to go intersate on work)

Electrically the K8055 can control the flow meters no problem as they take little current and it can also read it’s output, now all i need is a program to run on windows that display what is going on with the 2 flow controllers.

So what i need in the program is as follows:

  1. A box where i can enter the gas to be diluted concentration eg 1000ppm
  2. A box where i enter the desired value eg 500ppm
  3. the program would then wotk out the ratio of the gases needed eg in this case a 50/50 blend
  4. the program would then output the required voltages to the flow meters eg 2.5volts to each meter
  5. the meters will then set the flow rate and report back the actual flow rate being actieved e.g 2.48 volts
  6. the program will then convert this 2.4 volts into a concntration e.g 496ppm

Anyone that can help will really be gettign me out of alot of trouble.

Ian

5

Ian,

What level of accuracy and precision are you seeking in this application?

I ask because it is important to understand that the K8055 was designed as a hobbyist level experimentation platform, not as a precision industrial controller.

Regarding accuracy, it must be understood that not only is the K8055 powered from the host PC’s 5V USB connection, it also uses that source as the Vref for the ADC inputs–their output therefore will only be as accurate as the 5V signal from the computer’s USB port. Unfortunately for most PCs that is not particularly accurate–5.0V +/- 5%, 4.75V to 5.25V, per the USB specifications.

This can be overcome by using a more precise power supply, how precise depends on your needs.

Beyond that, the ADC inputs are only 8-bit channels, I.e. there are only 256 possible values across the 0-5V range, or 256 increments of approximately 0.02V each. This means at best that if in your application 2.48V is a distinctly different value than 2.47V it’s not going to happen. In practice only 7 of those conversion bits will be valid, making the 0-5V output resolution 128 steps of 0.04V each.

We next get to the analog outputs, they are implemented the PIC’s 8-bit PWM output passed through a single pole RC filter and buffered. While this a perfectly viable way of accomplishing DAC it is not the most precise or consistent manner of doing so and I would be surprised to find much better than 0.1V repeatability and accuracy in these outputs.

The K8055 is really neat device, I have had one for some years now and have another on the way, and it can accomplish a wide array of tasks–however it remains a hobbyist level device.

So, returning to my original question, what levels of accuracy, resolution, and consistency do you need?

Can you share the specs of the flow control devices with us (me?), it may well be that the K8055 can do what you need; however it’s always best to determine a project’s proposed components capabilities up-front rather than as a nasty surprise half-way through…