Nice work there ARO
Nice work there ARO
Former HWBOT and CPC World No1 Bencher
(highest rank ever: 1st at 05 Nov 2006 12:30, most hwboints ever: 331.7 points at 05 Nov 2006 12:30)
Voltage - The solution and cause of all your overclocking problems .
Please forgive my grammar and spelling - My Keyboard is dyslexic
Are the voltage readings from external probes, or direct from the card itself?.... if that makes sense
Originally Posted by margo bagginsOriginally Posted by JBARandomOWl: Any comments?
Bazx: You need to get out more
ARandomOWl: Thanks. That's the sort of comment I was looking for.
I've got the some of the circuit assembled on a breadboard so I can bring it with me to the meet No thermocouple readings for now, need a bit more time for that. I'm also having some issues with the second PWM channel so that's missing for now too.
Ok, so this has been put on hold for a while.
One PWM channel is working. The other isn't. It seems it is an issue with the microcontroller which is non-specific to my design.
The voltage reading are working. Although I need to work on the stability of the ADCs as the readings like to jump around a lot in practice. I think it may be to do with the wire length from the voltage source to my circuit.
I haven't worked on the temp probes yet. Need to get a concept drawn up.
Hopefully I will be able to work on it a bit more this summer
The unstable voltage readings seem to be caused by pickup (mains and other crap) along the length of the wire I am using between my circuit and the voltage source. I have used a software low pass filter to get rid of it and the reading is nice and clean now
I used software instead of hardware partly because it was faster to write the smaller amount of code than it was to find the components in my draws But also, it will mean I will have less components on the final PCB (cheaper, less chance of more noise getting in, easier board design).
Your rather good at doing gadgets like this.
Top work fella.
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Dave, you are correct. In general, a hardware filter is better (simpler, faster and better performing depending on the hardware chosen and the software algorithm used). However for this purpose a software implementation is rather simple and therefore fast. It's not like we are filtering audio (where usually rather complicated fft algorithms are used, not easy to do on a microcontroller). But we only want to cut off frequencies below about 50Hz, and that value isn't critical.
In simple terms, the performance (speed and quality) will be the same whether we choose a software or hardware filter.
I have done some testing and have found that putting a 10uF capacitor across the input of my ADC creates a good enough low pass filter in hardware (with the wire's resistance replacing a discrete resistor). So I think I am going to go with that for the final product and no software filtering.
I have also decided the thermocouple interface topology which will consist of an instrumentation amplifier and a linear digital temperature sensing IC which will serve for cold-point compensation in software.
Finally I decided that a lot of care must be taken in every stage of the PCB design to eliminate RFI interference from the PWM controller and reduce offset errors in the thermocouple amplifier to gain the maximum accuracy possible. This is project is serving both a useful purpose and a big learning experience in terms of circuit design and PCB layout.
Ok, it's coming along nicely now. Here is the complete schematic thus far Link
Still missing thermocouple symbols (not made them yet) and a couple of other minor things.