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Topic: How to use a DAC0808 with the arduino (Read 18109 times) previous topic - next topic

racemaniac

I wanted to experiment with a DAC, so i bought this little DAC0808 IC, found this nice little diagram of how to use it:

But when i wire it up like that... it does absolutely nothing. On pin 4 i measure 0.05V compared to the ground, and it doesn't matter what the input pins have, it stays at 0.05V (well, sometimes it goes all the way up to 0.07V, but that's not quite an improvement)
What i'm not entirely sure about is the 0V in the diagram (i connected this also to the ground).

And i'm just trying to get this DAC to work, my last test setup simply was this chip getting its 5V from the arduino, and the input pins directly connected to ground or 5V. No sketch or anything that could go wrong.

Boardburner2

#1
Aug 16, 2014, 05:03 pm Last Edit: Aug 16, 2014, 05:27 pm by Boardburner2 Reason: 1
Which package do you have , i think the pinouts differ

From the datasheet

OUTPUT VOLTAGE RANGE
The voltage on pin 4 is restricted to a range of ?0.55 to 0.4V when VEE = ?5V due to the current switching methods employed in the DAC0808.

I am unfamiliar with that chip but i thing this is possibly the case.

Try making vee a negative voltage.

racemaniac


Which package do you have , i think the pinouts differ

Full text on the IC:
M9736AD
DAC0808LCN
MC1408P8

From what i can find this is just a normal DAC0808, and the pin numbers from that diagram should be correct

Boardburner2

#3
Aug 16, 2014, 05:30 pm Last Edit: Aug 16, 2014, 05:35 pm by Boardburner2 Reason: 1
Cross post, see previous msg again.

If the package is dil and not surface mount the circuit should be correct.

runaway_pancake

#4
Aug 16, 2014, 05:33 pm Last Edit: Aug 16, 2014, 05:36 pm by Runaway Pancake Reason: 1

But when i wire it up like that... it does absolutely nothing.


Having to ask, since I don't know your skill-set like, but the dwg doesn't show the op-amp's power pins.
So, in case you did exactly what's shown and nothing more...
Do you have the op-amp's power pins connected (to anything)?

> > > adding dwg of my own
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

racemaniac



But when i wire it up like that... it does absolutely nothing.


Having to ask, since I don't know your skill-set like, but the dwg doesn't show the op-amp's power pins.
So, in case you did exactly what's shown and nothing more...
Do you have the op-amp's power pins connected (to anything)?
i'm currently wiring it without the opamp, just to see the result on pin4, once it does something i'll try to put an opamp behind it again (although, not even sure if it's required, from the datasheet, i see it has its own opamp internally as last step, and i found some diagrams that just skip the opamp).

racemaniac


Cross post, see previous msg again.

If the package is dil and not surface mount the circuit should be correct.

yup, it's a regular DIP package, checked with the datasheet to make sure the pinout matches this diagram (and measured every pin already a dozen of times to be really really REALLY sure that every pin is wired the same).
the only difference i have with the diagram is the resistors. don't have 2K resistors atm, so i tried with 1K and 10K, but googling circuits with this DAC, i find them with just about every imaginable resistor value... so i don't think that'll be the issue either. I've also got 3 of these dacs, so i tried switching it with another one to make sure it's not a defective chip, but the others do exactly the same.

what i'm currently wondering is: most diagrams show this thing being hooked up to systems that provide positive & negative voltages to pins 3 & 13 (like +12v and -12V), since i'm hoping to just use it with an arduino and without an extra power supply, i was glad to find the above diagram that simply uses it with 0 and 5V, but could that be the issue?

Boardburner2

0 to 5 v issue ?
Im not sure if i interpreded the datasheet correctly.

However have you a resistor from pin 4 to ground ?

Its a current output and a resistor is needed to develop the voltage.

racemaniac


0 to 5 v issue ?
Im not sure if i interpreded the datasheet correctly.

However have you a resistor from pin 4 to ground ?

Its a current output and a resistor is needed to develop the voltage.
that'll probably be the issue. First time i encounter a current output, it's indeed logical that you need to allow the current to flow. i'm gonna give this a try & hope it'll work :). (and i'll have learned something new today :) )

thanks for the help :)

runaway_pancake

The op-amp is configured as a transconductance amplifier, a current-to-voltage converter.


since i'm hoping to just use it with an arduino and without an extra power supply, i was glad to find the above diagram that simply uses it with 0 and 5V, but could that be the issue?


Two 9V transistor batteries make a dandy dual-ended supply.
In fact, you could "get by" with one for the negative supply (so you'd have a +5/-9V supply, big whip.)
Then decide what you want to do going forward (excuse the biz-speak.)
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

racemaniac

hmm, it's currently wired up with 10k resistors on pins 14 & 15, and tried with 1k, 10k and 100k resistors from pin 4 to ground, but it makes no difference, stays at 0.05V >_<

so still no luck :(

Boardburner2

As pankake has shown the op amp deeds a dual rail supply

racemaniac


The op-amp is configured as a transconductance amplifier, a current-to-voltage converter.


since i'm hoping to just use it with an arduino and without an extra power supply, i was glad to find the above diagram that simply uses it with 0 and 5V, but could that be the issue?


Two 9V transistor batteries make a dandy dual-ended supply.
In fact, you could "get by" with one for the negative supply (so you'd have a +5/-9V supply, big whip.)
Then decide what you want to do going forward (excuse the biz-speak.)
i know that's an option. Is it really required though? i know i should learn a bit more about opamps so i could answer questions like this myself. The diagram i posted above suggested that it's possible without having a -5V, but maybe it's incorrect?
(i've also found a solution that uses 0 , 2.5 and 5V as inputs, with the 2.5V being the "ground" to simulate negative voltage without actually needing a -5V, but that's a lot of voltage dividers to do it on all those pins >_< )

racemaniac


As pankake has shown the op amp deeds a dual rail supply


okay, thanks, then i'm going to experiment with adding the -9V as suggested, lets see if that brings things to life a bit :)

runaway_pancake

I'm not good with the DAC IC's VEE being at 0V/Gnd (missed that) either.

I vouch for my design shown.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

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