How many orifices do I need

[Kimi]

Hi Old Grey,
The chip is an Atmel atmega644, the sensors are from freescale.

With the atmega you have a 10 bit adc, and this can be easily oversampled to give a 12 bit resolution.

If the sensor is a gaugetype giving 5 volt swing of 10kPa, you will get about 10kPa/4096 in resolution.
If the sensor is a diff type it will give 5 volt swing for -10kPa to +10kPa. that will give 20kPa/4096 of resolution.

If the Testpressure is 28 or 40", you will never need a sensor more than 16" at the orifice, and if you get beyond that, you just put in a larger orifice. Selecting a correctly rated sensor will help you to get the whole sensors swing to usage, increasing accuracy. 16" is about 40% of 40", so you will loose more than half of your DAC capability if installing a wrong rated sensor. If you put in a 100" (7025 sensor), you will loose more than 80% of you ADC range at the orifice, and the system is close to unusable in a flowbench.

The maximum pressure these can withstand is about 75Kpa (300" h2o), when broken you will get distorted results, witch must be catched at the calibration stage.

And also remember, you cant fix or correct mechanical issues with a digital meter.
You can make your life easier, but it will not make your bench any better.

/Kimi

M. Xmas

[Kimi]

Hi,
This is for the 7007 Diff sensor.
When you get 1 bit change in the ADC with an orifice of 2" (5080 in mm*100) and the testpressure is close to 28"
and the orificepressure is about 16", you can see from the chart what is the minimum changes in the CFM reading

If you have the 7010 or 5010 gaugetype, and the voltage span and the ADC is 10bit, you calculate

CFMdifference /7*10/2 f.ex (211.50-211.06)/7*10/2= 0.31 cfm , if you have the 40" sensor, the resolution is 1.24cmf

The number two comes from that the 7007 is a -7 kpa to +7kpa sensor.


With 4x oversamling this resolution can be divided by 4. To get oversampling to work, you must at least remove the condensators from the sensors powerfeed and make changes to the atmel ADC read function.

/Kimi

[Old Grey]

The sensor is the Motorola MPXV5010DP

http://www.datasheetcatalog.com/datashe ... 10DP.shtml

It's mainly the IC that I'm interested in.

The manufacturer sanded the numbers off so that no one knows what it is, and because it's so old, 2007, I wanted to see if I could add averaging to the programming.

I was thinking it was some sort of PIC, mainly because it's old and the Atmel atmega644 seams too advanced for back then, but I'm not sure as I'm no expert and only assume that the PIC came before ATmega.

http://www.flowperformance.com/fp1.html

http://www.flowbenchtech.com/forum/view ... ?f=3&t=638

My limited catalogue say that there is one 40 pin PIC - PIC16F877A I/P, and one PIC18F4550 - It's USB2 so may be latter -, but five ATmega's. Is there any way to tell which one based on what pins are connected to the other components.

[Tony]

My limited catalogue say that there is one 40 pin PIC - PIC16F877A I/P, and one PIC18F4550 - It's USB2 so may be latter -, but five ATmega's. Is there any way to tell which one based on what pins are connected to the other components.

There are a great many microcontrollers out there spanning a very long period of time, some versions fairly obscure.
These also date very rapidly, and older versions can be difficult to obtain once obsolete and out of production after only a few years.
The 40 pin wide body DIP package was pretty popular for most of these as well, especially the older types.

Even if you can identify the chip, the chances are that it has a security bit.
Whoever made this "thing" went out of their way to make it difficult to copy by sanding off the type numbers, so having a security bit in there and activated would be pretty certain.

What this means, is that you program one of these older chips with a fairly standard EPROM type programmer. The EPROM programmer can then read back the program you have just downloaded into the chip to ensure that the programming was entirely successful.
Next step is to program the security bit in the same way all the other memory locations have been programmed.
Once that security bit is set, it locks you out and the internal program can no longer be read from outside the chip.

No chance of reading it, duplicating it, or doing anything at all except just powering it up and running it in the normal way.
Even if you can source another identical chip, the EPROM memory in it will be blank and totally useless.

Later microcontrollers now use flash memory not EPROM, and many of the pins are software configurable as to function, making identifying the chip by pin function almost impossible. These also have a security feature to lock out the software thieves.

Sorry, but I think you are pretty screwed trying to duplicate this.
Much easier to start totally from scratch anyway.

[Brucepts]

The original design on that DM dates back to 2002-2003 time frame and was based on serial output. I would venture to say that what was used back then is still being used now as far as chips. I had to sign a non-disclosure agreement when I was working on the design with John. I was working more with the flow elements than the DM but was field testing it and giving feedback.

I still have all the email traffic incase I needed it for any reason as some of my design elements ended up in the patent and I was also making my own elements at that time. I have no info on the internal DM design though.

[Kimi]

Hi Old Grey,
It is an Atmega644 or its predesessor, atmega32. These are pin compatible, 644 has twice the memory.
Through the ISP connector and the AVR studio, you can upload the fw from it, run through the disassembler
and the rewrite the stuff in C. Very heavy work, and I don't encourage to do that.
I've done that for a company that had lost their sourcecode, it took a couple of month to recreate it. The FunFactor was 0.

Usually those kind of designs don't have the fuses burnt that protects the sw. If the protection fuses are burnt.
it's mission impossible to upload or download nothing to the chip.
If there is an arduino boot loader in it, you simply connect it to the serial port and download the sw using avrdude.
If not, you have to connect the ISP connector to it and download it using f.ex AVRISP MK II or similar.

The chip costs about 10$, it was announced sometime in 2005 and is still available.

You can write your own sw to it. the Sensors are connected to ADC7,6 and 5.

It's a nobrainer to reverse engineer that and write new sw to it. It's an other story if there is any sense doing it.


The issue you will run into, is that you must create the sw from scratch + the protocol between the pc and
then write a pc program for it. It takes a month or so

If it works, there is no sence to destroy it. The hw parts value is close to nothing, but as ready device it is more valuable.

/Kimi

[Tony]

Usually those kind of designs don't have the fuses burnt that protects the sw. If the protection fuses are burnt.
it's mission impossible /Kimi

That's the problem.
This guy deliberately sandpapered off the part number to hide the chip type.
He would not bother to do that, and still leave the firmware fully accessible if it can be very simply locked with a couple of keyboard strokes.

I have been on both sides of this.
Trying to get inside protected engine management software to try to change things around a bit.
And at times, effectively keeping less than honest people out of some of my own interesting little commercial projects.
They were very angry too, when they discovered that my ideas could not be so easily stolen.

[Old Grey]

I don't really want to reinvent a DM and don't really want to build this flowbench, it's just a means to and ends to learn more about engine design when there is no money available - DIY is cheap when your labour is free -.

My only knowledge programmable proms was from 1990 when I friend working for Ford showed me one of the first that came on the market - it was very simple-, and if they now have all this security added I'm not even going to look into it any more.

Thanks guys, it was a whim of and idea and now just seams too difficult so I will stick with the FP1 that I've got.