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Newbie need project help..

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Marcus_uk

New Member
Hi,
I'm new to electronics but have a basic understanding of how it all works. I want to convert a 5V dc signal into a different 5V dc signal. I have an input to output graph which i wish to impliment on the signal. What is the best way to do this? adc then maybe an eprom?? then a dac? Please could someone tell me exactly how this can be done.

Cheers,

Marcus
 

Noggin

Member
a wire does pretty good when converting 5dc to 5dc :) If you can show the graph it may be easier to help. It be accomplishable with some digital logic.
 

Marcus_uk

New Member
Hi,

I'm trying to modify a sensor output from a mass air flow meter on an engine, which has a range of 0-5V D.C.
I wish to modify it in a non linear way so i can't use a potential divider. Unfortunatly i don't have a copy of the graph on this pc but i've drawwn a rougth idea if what is needed on the attached file.
 

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bmcculla

New Member
Hi Marcus,

I've heard of using an eeprom in just the way you talked about. The concept you are talking about is called a Look Up Table. While the EEprom will work dealing with the logic to implement the correct timing might be more trouble than it's worth. A microcontroller will let you do this same idea but remove a lot of electronics allowing you do do mostly software- which is a lot easier for a beginner.

Another posibility, since your graph looks like an exponential curve, would be to use a logarithmic amplifier. A logarithmic amplifier is just an op amp with a Diode or bipolar transistor in its feedback loop. Some tuning would be reqired but it might work.

A note about your wording: when you say volts DC that means it doesn't change- like a power supply. What you mean is a signal from 0-5V.

Hope this helps.

Brent
 

Noggin

Member
This is what I've come up with. The transistor is an NFET, though I do NOT know the characteristics of what PSPICE models it as... such as doping, length, width, etc. It would probably also be more efficient to use a PFET and an inverting opamp instead of PFET and non-inverting opamp. And all I know about the opamp is that PSPICE models it with a gain of 1x10^6 and I put the power voltages at 5v and 0v instead of 15 and -15. Lastly, V1 that says 0v is your changing input voltage.

I'm gonna go watch star trek :)
 

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Noggin

Member
since its commercials, this is what it looks like if its 1:1 scale for x:y
 

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bmcculla

New Member
Hello again,

Noggin - You have a nice exponential generator but marcus needs to linearize his exponential raw data. If you replace R10 with the transistor you should get a nice log function that could be used to turn a exponential input into a nice linear output.

Marcus - A good development kit and data sheet is the best way to get started with microcontrollers. I'd recommend Cygnal's Kits for pure ease of use if you just want to get some experience with microcontrollers. 8052.com is a good resource for this type of microcontroller. For your application Cygnals controllers are probably overkill. Check out Atmels AVR series- good and cheap. Digikey.com is the best place to get both of these.

My other advice is to spend the time to learn C rather than basic or assembly. Its not that much more compilcated and much more powerful and flexible.

Brent
 

Noggin

Member
Atmel AVR's are great and there is a forum dedicated to their use and it is of GREAT help to people just getting started. www.avr-freaks.org

I would suggest, if you go that route, that you get an STK500 development kit, it'll come with a microcontroller that should work for you. However, the STK500 is gonna cost you about $100 to $150.

OH MAN!!! Digikey sells the boards for $80! I paid more than that buying them through an acquaintance that works for Atmel. Drats....
 
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