Some EE opinions please

[Groth]

Explains the recent rumbling in my belly... I'm full of bee's knees.

Ah, I had forgotten about that software and their project (with the stupid pdf that still won't work right for me). Handy cool stuff once the back row of p-port signals are wired how they use to be.

So where's that PWM?

[Groth]

Originally Posted by Incoherent

what does p-port pin 17 actually do?

Should I leave the DGND unconnected to the AGND?
Is it worth spreading the ground around the place?

The control byte is at p-port address+2; /C0 is pin 1, /C1 is pin 14, C2 is pin 16, and /C3 is pin 17. I've no idea why three of the four are inverted.

I'd keep DGND as it is, but reserve the option of solder-bridging it to AGND if things are funky. (I learned that 'keep the options open' from you )

Widening the ground under the ADC would be cool, maybe even run a ground trace under it on the top layer. Large scale ground-pours? Eh, up to you. I don't think it'll make a measurable difference, but it won't hurt.

[Incoherent]

Originally Posted by Groth

So where's that PWM?

How about this. DAQ_PCB6_pwm.pcb and DAQ_schematic6_pwm.sch.

Good to have it on board, I don't need to use it initially if I don't want to. Frequency and amplitude settings are component values I'll play around with a bit.
This is final pending no mistakes or better solutions found over the next few days.

[Groth]

A few inconsistancies between schematic and PCB. As is, the PWM won't work.

Edit: Superfluous exposition elided.

[Incoherent]

Originally Posted by Groth

A few inconsistancies between schematic and PCB. As is, the PWM won't work.

Damn it. A mistake there. I haven't considered your suggestions yet but the glaring error is that the inverting input to amp4 U1 pin13 should be fed from amp2 U10 pin7 integrator OP. NOT pin 2-5.

U1 is the comparator. U10 is the triangle wave generator. A near exact copy of this from Maxim. Only component values will be different.

[Groth]

Hmm, yeah that'll work. Different way than I've seen before, I hadn't though of offsetting/compressing the triangle wave. Cool.

For what it's worth, some combinations of settings for VR1 and VR2 will stop the oscillator.

[Incoherent]

Originally Posted by Groth

Hmm, yeah that'll work. Different way than I've seen before, I hadn't though of offsetting/compressing the triangle wave. Cool.

For what it's worth, some combinations of settings for VR1 and VR2 will stop the oscillator.

Well, as you've spotted, it lets me use the raw temperature level untouched. No gain stage. Reducing the amplitude of the TW increases the effective gain and the bias is the set point.
Not a very conventional approach I guess but in my Excel model it works. I think I'll have some fun with settings before I get something stable.

[Groth]

Yup, the more I think about it, the more I like your PWM. Compact, subtle.

I retract all the good things I said previously in reference to surface mount ICs. I just spend a couple hours fighting with a 10 lead micro-SOIC monster (0.3 mm leads on 0.5 mm centers). I hate it when I can't run traces between an IC's legs.

[Incoherent]

Indeed. The first 186 sample that Maxim sent me was one of those but 20 lead. I flapped around with it a bit before deciding that the SO 1.27mm pitch was the smallest I could contemplate. They were good enough to send me a DIP package as well.
I wonder if there really is any real space gain from using these small chips. The external components need to be further away relatively in order for the leads to have the room to flare out and connect. Plus as you say, there is no room for traces between legs.
I guess its all 4 layer and up.

[Groth]

With access to reflow soldering and plenty of plated-through vias, they're great for space saving. Us poor hobbyists have to make due with with crude solding irons and boards etched in the kitchen sink. :shrug: The board I was working on ended up 30x70 mm; it'd be tough to put 130 pins worth of through-hole in that space.

SOIC/1.27 is my favorite. Small, but big enough for a between-the-legs trace. You do know you're required to make something with that SSOP Max186.

[Incoherent]

I have decided to bite the bullet and use the ExpressPCB service so now the boards are on the way to me. Unfortunately I ordered the PCB with the PWM trace error in it. Fortunately it is a very easy board fix, the trace in question run right past the pin it is supposed to connect to.

Now I am assembling a bill of materials and would like some opinions on a suitable PWM frequency for driving fans. As I have it it is running between 250 and >1200Hz depending on gain setting. Is this reasonable?

Some raw specs based on current component values:
Voltmeter 0-23.34V, +/- 2.9mV
Ammeter 0-11.9A, +/- 1.5mA
Giving a Wattmeter 0-278W +/- 0.009mW
Accuracy unknown, component values will be 1%.

4 temperature channels
-40-150°C +/- <0.2°C
0-85°C +/- <0.025°C
18-55°C +/- <0.015°C

2 high resolution temperature channels
15-35°C +/- <0.0025°C

Accuracy unknown, subject to component drifts, tolerances, noise control and accuracy of calibration reference. Who knows? I'll see how the oscilliscope, data noise and repeatability look when it's done.

[bigben2k]

Nice work!

Do you have any idea if you could gain more accuracy from having two temp channels measured in differential mode?

Otherwise, I just might join you in this setup. Let us know how it works out, ok?

[Incoherent]

Originally Posted by bigben2k

Do you have any idea if you could gain more accuracy from having two temp channels measured in differential mode?

Probably could. Differential inputs would normally be preferable but for the fact that this particular ADC does not use a true differential mode. This pseudo-differential mode I was not keen on messing about with, it can give some snapping problems at certain input values apparently.
Also I did not want to "waste" two ADC channels on a single input.

With a bit of software I could actually use two of the thermistor channels as they are in differential mode and obtain a delta T reading directly, for example for the water sensors. This might be a more accurate way to get the critical delta Tin-Tout for heat-to-water power calculation. Less sensitive to thermistor ref voltage noise. But a bitch to calibrate.

[Incoherent]

The PCBs arrived today. Three of them. $51. yikes. shipping $44. Holy SHITE!!



Also Texas Instruments have an even better samples program than Maxim, I got six INA122's from them, three day shipping from US to Sweden. Amazing.

This mean's that all the Semiconductors which would have cost me in excess of $120 if I had bought them from a local supplier are free samples. More than makes up for the PCB cost.

[Groth]

Originally Posted by Incoherent

Now I am assembling a bill of materials and would like some opinions on a suitable PWM frequency for driving fans. As I have it it is running between 250 and >1200Hz depending on gain setting. Is this reasonable?

A little late but :shrug:

As part of testing out a function generator I just got from the junk shop, I hooked it up to give me a dial-a-frequeny PWM. The whole range of 1 Hz - 100kHz worked; the sweet spot for low noise and wide duty cycle range seemed to be ~900 Hz.

[BillA]

be interesting to get a ballpark on the PWM added noise vs. the reduction in fan noise
gonna be different though for all fans apparently

[Groth]

Silence isn't goal, controlling the water temperature is. Not having the fan screech is nice, but having it willing to run at <20% duty cycle is more useful.

Bill, my sample of three fans all had different ratios of turbulence noise vs. PWM noise. Total noise seem to decrease (measured with an uncalibrated ear) with reduced duty cycle, but noise vs. CFM certainly increased.

If control weren't the big issue, I'd say 25 kHz or more. And maybe pulse between 12V and 3V (not ground), so that the fan's electronics would stay powered. Projects for another day.

[BillA]

Originally Posted by lolito_fr

deleted
10 chars

I don't think it was gibberish, that's what many report - no ?

[lolito_fr]

be interesting to get a ballpark on the PWM added noise vs. the reduction in fan noise

My statement was based on "insufficient data". Was forgetting that PWM allows lower RPM than DC.

[lolito_fr]

(sorry for the threadjack)

groth, my remark was more an off the cuff reaction to Bills' comment - and applying more to the general case of manual speed control. Sure, if you're using some form of PID and want accurate temperature control, then PWM is convenient + efficient and will also get you less non linear distortion.

Backing up my initial statement that PWM is a bad solution if you are a noise freak, I would add that if you need to run your fans at 20% then maybe swapping them out for lower speed versions would buy more dB Otherwise just filtering the PWM output with a cap would work, I guess.

[Groth]

Not my thread, hijack away!

Yeah, I figured that you (and Bill) were thinking of the general case of speed control. I don't expect everyone to keep track of the the details of every thread, hence my pointing out control was the overriding goal. Never meant to sound harsh or dismissive. I agree completely, PWM isn't for the noise freaks.

To continue farther afield...since the fan motor has some inductance, once you add your capacitor on the output, all you need to add is a freewheeling diode to make a crude switchmode supply.

[Incoherent]

An update.

Basically the last few weeks have been spent ironing out little faults, (a bad solder joint, a 2 1/2 year old's intervention which blew the digital circuitry etc)

I have connected the digital ground to the analog ground. There was an offset in the raw output of about 4-5 LSB with it disconnected with noise levels the same so I figured it should be there.

I have spent a fair bit of time generating Steinhart-Hart coefficients for the thermistor calibration. I have done this by using 0.01 deg C (crushed ice and water), 100 deg C (boiling point) and ~37 deg C (water at about body temperature as measured using a medical thermometer, multiple samples taken as an average). This has generated curves for the four low resolution channels which ensure that they agree to within +/- 1LSB (~0.025 deg C) when taken as an average, over a range from ~20-55 deg C.

I am amazed at how well this unit works. I need to check linearity but I am confident that the S-H calibration coefficients are giving a good result, it is an industry standard method and typically has errors of less than 0.01 deg.

This document has a lot of very useful info.

I have made a new fluxblock. It has 3 sensors spaced 5mm apart to check the linearity of the measured heat flux. This one is 12x12x12mm, a 10x10x12mm version is planned. I have also made a matching heat die with one sensor. This will allow me to finally measure the TIM resistance with a fair amount of precision by interpolation.

Two water sensors, with a resolution of <0.005degC will let me crosscheck power to water vs power to WB vs Power to heat die. Secondary and tertiary losses will come from these numbers, curiosity only, no practical value, only applies to this setup but interesting to see the effects of insulation.

Still haven't played with the PWM circuitry, it will come.

[bigben2k]

Very cool... rest assured I'm keeping a close eye on your progress!

[bigben2k]

...and sure enough.

I picked up a six-pack of AD7713AN
"CMOS, Low Power 24-Bit Sigma-Delta, Signal Conditioning ADC with Matched RTD Current Sources"
http://www.analog.com/en/prod/0,2877,AD7713,00.html

...and two AD580 and two REF192FS.
http://www.analog.com/en/prod/0,2877,AD580,00.html
http://www.analog.com/en/prod/0,,769_838_REF192,00.html

Now...

I've already got too many things going on (as if no one knew!) so this is probably going to sit on ice for a while, but I thought I'd put the offer forward; if anyone is interested in building a similar circuit, I'll supply the ADCs and the volt references. Heck, I'll even cover the cost of the PCBs.

[jaydee]

Pretty interesting read here. ben linked it from another thread and just got around to reading it. This reminds me of another DAQ based on the maxim186 I cam acrossed called the MiniDAQ. http://www.embeddedtronics.com/Electronics.html

Anyway my question to Incoherent is what software are you using with it. Sorry if I missed it.