hello friends,
can you give name of a low cost commonly used 4 bit analog to digital convertor ic ....which can be used with a transducer.....

 

Don't know as I've ever seen 4 bit ones? - as with most such requests, it's probably easiest (and cheapest) to use a PIC to do the job anyway!.

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Search for "R-2R" DAC - 8 resistors and an opamp

 

It's very hard to answer your question with out knowing the environment for the device and how you intend to use the data. are you going to use this with a microcontroller? as nigel implied, many have built in ADCs. If you are stuck with one that doesn't have an ADC, use the RC time constant and measure charging time of a cap.

how many specific values are you looking for? for a small number, you could use a comparator (and many uCs have comparators built in, also).

there is a huge universe of ADCs out there with all sorts of different interfaces (parallel, I2C, SPI, ...). I suggest looking at 8 bit ones as they will be the cheapest and you can ignore the lower 4 bits.

 

It's a picky point, but that's a DAC. He asked for an Analog to digital converter. I've never seen a 4-bit one though.

 

actually, I believe he is suggesting a sucessive approximation style ADC but that takes 5 pins. that's why it needs the opamp (comparator actually), I think. RC time constant approach takes one (though it has to be switched between in and out).

 

An R-2R ladder and an opamp is a voltage output DAC. How did you leap from there to an SAR A/D converter? the original poster asked for an A/D converter IC, not a build it from pieces SAR. Nobody's done that for decades.

My two cents:
MAX7224 its 8 bits and you can hook it to any bus. If you want I2C or SPI serial interfaces then Maxim has those also. Check out Texas Instruments, they make nice parts that complement their line of DSP's

 

I misread the question - I've never heard anyone ask for a 4 bit ADC. At that level the RC timing circuit (or
one of it's relatives) is the way to go.

James

PS, that said, I can at least save some face by saying (like philba mentions) that you can use a DAC and comparator(maybe a on-chip one) to do a faster ADC conversion - inside 4 clock cycles, (binary, SAR style) than using a RC timing loop.

 

2^4, that's only 16, so it'd be really easy to build one with 4 quad comparator ICs and some diode-transistor logic.

You set up the 16 comparators with 16 different voltage referances. The best way of doing this is with a voltage referance and a potential divider. Now you'll have 16 different outputs, eah will output a high when the reference level is reached, you need to configure your logic circuit so it'll output the correct 4-bit binary value when the input goes high.

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wow, gettin touchy there, pb. as james said, its pretty straight forward, not much of a leap at all. especially when you can do either with that bag of parts.

 

I have Of course its always a hassle to build things from basic components..but if its not a critical system, and the original poster didn't know much about ADC's, its a great way to learn. Theres many 'leaps of the imagination' there, but hey, might be of some use. Something that may be easier than even an SAR, but still interesting (no offence to the comparators idea) would be the brute force approach....a simple 4-bit binary counter, and a comparator.

Assuming you can't get a 4-bit ADC (I've never seen one tbh) building one isn't that daunting...

For 4 bits, it'll only take 16 clks, and with a CMOS/TLL counter we're talking MHz. Of course, for high resolutions the counting becomes a lot longer, but 16 clks (4-bit) isn't that bad. With your analogue input (0-5V?) into the comparator, your counter's 4 outputs to a 4 bit R-2R ladder which goes into the other comparator input (I'm sure many know how an SAR ADC works). The comparator output latches a flipflop which stops the counter, and also acts as a 'done' line, and you just read the counters outputs for your digital value. This FF can be reset to start another conversion.

Actually, I'm gonna try this as a quick experiment, can't say its 'fun', but its definately interesting, seeing as the input range (assuming we use the LM393 and of course an opamp buffer after the R2R) can be pretty big, and completely variable. So theres a 'Vref'. Also with the speed it could run at on its own clock, 1Mhz sampling frequency shouldn't be a problem. Well, a lot of hassle, but a stripboard, 2"x1" 4-bit ADC might come in handy one day (even though I'm surrounded by PIC's with ADC's coming out their ears )

just a few thoughts,

Blueteeth

ps. super easy option? Use a standard 8-bit ADC, and only use the 4MSB's, discard the lower nibble. Not ideal, but you'll have 16 'levels' of voltage to measure. (you'll need to correct the input voltage level).

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Use a cheap 8 bit converter and throw out the lower 4 bits.

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That is indeed a simple A/D, but it is not a successive approximation A/D. An SAR A/D only requires N clock cycles, not 2^N.

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Ron

 

You're right, it isn't a SAR, but I didn't say it was.

'Something that may be easier than even an SAR'

I just used the SAR reference because the circuit is almost identical, comparator, DAC etc.. but the algorithm it uses it obviously different.

Its a pretty similar circuit setup, just not 'successive approximation', its the 'brute force' approach. Sorry if I didn't make myself clear. I have built a SAR ADC, back in uni, but we were asked to come up with a similar alogrithm that uses the same circuit (working with CPLD's back then) and simply 'counting' was what I came up with, woefully inefficient, but doesn't really require any 'intelligent' logic, and is therefore cheap and easy.

Blueteeth.

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Sorry, Blueteeth. I reread your original post. You did say "Something that may be easier than even an SAR, but still interesting (no offence to the comparators idea) would be the brute force approach....a simple 4-bit binary counter, and a comparator. ". I guess I skipped over that and jumped to an erroneous conclusion.

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Ron