Universal PI Micro

[Wirechief]

Hi Bugwiskers, I have gotten in a bit late on your project. I wonder are you going to selling boards for the project when all is checked out? I hope you will keep going with it and look forward to your results in a complete unit. Ok God Bless and good luck. I am going to try and keep up with your project. Thank you BW.

John Tomlinson,CET
John's Detectors

[bugwhiskers]

Hi BjBj,
The decay curve CRO shots are of the old bus prototype using the ATMEL chip. The noise and the difficulty for forum members to make the boards caused it to be defunct.

The samples will be taken at about 5ms intervals. How much would you expect the temperature to change in 1/200th of a second ?

You really need to take me up on my offer of a video of the stability of the platform.

If my tone seems harsh it is probably because I have asked you before to offer alternatives if you don't like the current direction. Constant criticism when you haven't seen the proof or offered an alternative is a bit hard to take.

regards
bugwhiskers

[BJBJ]

Hi BjBj,

The pics show the 80mV noise in the decay curve of the bus prototype. Adding filters to diminish it also reduced the usefull signal and therefore sensitivity. The forum members that voted also requested a ready made platform and the one chosen is shaping up well..... you can see for yourself if you care to look at the video.

regards
bugwhiskers

I do care to see videos if i could, no need to be short in the tone!

Now im perplexed!!!

Which detector are the pictures from ?

The one with 10bit AVR MCU and 24mux sample channels or
from the Aduc with 24bit ADC and 24mux sample channels?

Besides how much of that decay curve are capacitance gate charge?

regards
BJBJ

[BJBJ]

bugwhiskers;

>I am a bit perplexed. You want to see the noise from a defunct platform >and you don't want to see a video of the new platform working well.

I wouldent mind see it, its just that im on a very slow modem line
to the net. Thats all!

Why is it defunct?

>Because the software compares the relativity of the samples to previous >ones, drift due to temperature doesn't matter.

?
The samples after the previous vill drift to.

>Most PI circuits use a 555 or similar for the audio. Because the 555 is >connected to ground, any change in threshold from earlier stages will >necessitate some sort of constant adjustment if the audio threshold is to >remain constant.
>If relativity is used it generates a number that is fed to the micro's internal >PWM for the audio and drift due to temperature or whatever is no longer >part of the equation.

Im not talking about the audio detector side of it, im talking about all the components that are involved in your new detector, the mux, the caps etc.

Rds of the mux will vary for instance. The idea are, calibrate it away!
Im talking about the ide of yours to use 24bits of resolution, or even
16 bits are a pain to reach in an enviroment that changes.


regards
BJBJ

[bugwhiskers]

Hi BjBj,

The pics show the 80mV noise in the decay curve of the bus prototype. Adding filters to diminish it also reduced the usefull signal and therefore sensitivity. The forum members that voted also requested a ready made platform and the one chosen is shaping up well..... you can see for yourself if you care to look at the video.

regards
bugwhiskers

[bugwhiskers]

Hi BjBj,

I am a bit perplexed. You want to see the noise from a defunct platform and you don't want to see a video of the new platform working well.
Because the software compares the relativity of the samples to previous ones, drift due to temperature doesn't matter.
Most PI circuits use a 555 or similar for the audio. Because the 555 is connected to ground, any change in threshold from earlier stages will necessitate some sort of constant adjustment if the audio threshold is to remain constant.
If relativity is used it generates a number that is fed to the micro's internal PWM for the audio and drift due to temperature or whatever is no longer part of the equation.

regards
bugwhiskers

[BJBJ]

In what way should i intrepetet that?

Good or bad?

Bad if its 24 bits, good if its 16bits?

What pot are you using a +100ppm ,50ppm, 1ppm?

Your test are at home in somwhat controlled enviroment step
out into the your Aussie desert at 50deg c for aminute os so
and expose the ADC/Mux/Caps/resistors ,etc to the heat and
it will change.

Better yet put in a LM 35 or similar and continuely read it and calibrate
away the temp change to the sampled coil value!

Btw if you have still pictures from scope of the sample noise it would be nice!

[bugwhiskers]

Hi BjBj,

I did even worse than that, I put a wet finger on the adjustment pot leads and the 4 digit noise was evident. Remove the finger and the numbers return to exactly what they were, about 5 times in a row this was performed.

I can email you the video if you want.

I must admit I had trouble believing it also but a picture is worth a thousand words and a video even more.

regards
bugwhiskers

Attached is the source file containing the LCD screen driver with leading zero blanking. The extension has been changed from .asm to .txt to allow me to post it here.

The program takes 4*24 bit samples from AIN1 to AIN4.

At the moment it is set up for the fastest possible sample time and I am staggered at just how stable it is. Mind you, it is being fed from a string of resistors hooked up between +REF and AGND.

regards
bugwhiskers

Breath on the string and watch the numbers!
BJBJ

[bugwhiskers]

For the code hungry.

Attached is the source file containing the LCD screen driver with leading zero blanking. The extension has been changed from .asm to .txt to allow me to post it here.

The program takes 4*24 bit samples from AIN1 to AIN4.

At the moment it is set up for the fastest possible sample time and I am staggered at just how stable it is. Mind you, it is being fed from a string of resistors hooked up between +REF and AGND.

regards
bugwhiskers

[bugwhiskers]

Changing the input to the pot from AVDD to REF+ has reduced the noise to ~200. The test was done with the fastest conversion speed which also has the worst noise.

regards
bugwhiskers

[bugwhiskers]

The routine to get an AtoD reading onto the screen is working as can be seen in the photo.
Leading zero blanking is working and if the input number is zero the last zero is left intact.
Notice some jitter on the second last digit. The input is being fed from a 10 turn pot connected between AVDD and GND. After watching it for a while I concluded that there is a jitter of ~ 1000 without any digital filtering or S/W averaging.
The next step is to hook up the multiplexers, pre-amp and coil drive circuitry.

regards
bugwhiskers

[bugwhiskers]

Hi BjBj,

The Evaluation board is available from any worldwide Analog Devices distributor for around $75US. It comes with a full IDE for assembler and also a Simulator that works. There is a "C" kit available but it is a lot more expensive.
There are code examples for the 8051/2 everywhere on the web and the instruction set is easy to learn and very efficient.

Today I hope to finish the routine that takes the 3 byte output from the AtoD, converts it to 8 digit ASCII (with leading zero blanking) and displays it on the LCD screen.

regards
bugwhiskers

[BJBJ]

[quote=bugwhiskers;54267]Hi BjBj,

>All R&D work is try it and see. A few things are certain, the AtoD must be
>inside the micro so that external transfer overhead doesn't slow things up.
>I am going for the maximum number of bits and then see what is left that
>is usable.

Well, as mentioned previously INL has already eaten up some bits
even before you actually have powered the Aduc device up!
So regarding to that specific value there is no need for test and see really.
But i do understand your approach, i would have done the same.

>Another certainty is the low cost and ready availability of these evaluation
>boards. The PGA and digital filtering is also a very big plus for the
>ADUC845, it will allow software programmable gain and possibly elimination
>of certain noise bands. Don't forget, the AtoD will be reading the voltage
>on a cap which is static and I can interlace the readings to allow for the >best possible result.

>I do appreciate all input BjBj, afterall, this is not a commercial project and >I expect to make nothing out of it except a detector that will do what I >want.

I really hope you succeed, because if you do you have a buyer
of the kit over here!

>Knowing how the sampling works, perhaps you could provide an alternative
>method to achieve the same objective, I assure you my ego will be totally
>unaffected as I am under no illusion that I know everything.

Well, i hardly know anything i just try to help out!

At the moment your multiple sample cell idea is a very good solution i suppose.
There is always the direct sampling with video ADC plus a FIFO or fast ram but
that will eat battery power and you need a micro with a fast access bus to external
ram, all a bad idea.

>The attached pic is of the Evaluation board running a 40X2 LCD.
>Now I can start doing some sampling and see just how many of those 24
>bits are realisable.

Splendid!

I think your doing great BW, i just try to see all sides of the subject in
a way to help out even if it might sound harsh sometimes but reading
data sheets that promises gold and glory raises my suspiciousness a bit.

There are plenty of bonuses with the Aduc to test it to see where
it ends and i don't think you need the 24 bits even 16 bits would do
more then fine if its achievable.

How much did you pay for the starter kit, and what tools do you use?

Regards
BJBJ

[bugwhiskers]

Hi BjBj,

All R&D work is try it and see. A few things are certain, the AtoD must be inside the micro so that external transfer overhead doesn't slow things up. I am going for the maximum number of bits and then see what is left that is usable. Another certainty is the low cost and ready availability of these evaluation boards. The PGA and digital filtering is also a very big plus for the ADUC845, it will allow software programmable gain and possibly elimination of certain noise bands. Don't forget, the AtoD will be reading the voltage on a cap which is static and I can interlace the readings to allow for the best possible result.

I do appreciate all input BjBj, afterall, this is not a commercial project and I expect to make nothing out of it except a detector that will do what I want.

Knowing how the sampling works, perhaps you could provide an alternative method to achieve the same objective, I assure you my ego will be totally unaffected as I am under no illusion that I know everything.

The attached pic is of the Evaluation board running a 40X2 LCD.
Now I can start doing some sampling and see just how many of those 24 bits are realisable.

regards
bugwhiskers