interfacing a DAC0832 to PIC16F877

[tyron123]

is there a way to interface the DAC to the PIC .... kinda new to these kinda stuff ... i need a analog output from the PIC so i thought i'd use a DAC, but my problem is now about the data lines.. and other pins connectivity... ne ideas?
any help is appreaciated
Tyron

 

[Nigel Goodwin]

is there a way to interface the DAC to the PIC .... kinda new to these kinda stuff ... i need a analog output from the PIC so i thought i'd use a DAC, but my problem is now about the data lines.. and other pins connectivity... ne ideas?
any help is appreaciated
Tyron

An easy (and cheap) way to make a DAC is an R2R ladder, MicroChip have an application note about it. I'm not familiar with the DAC0832, but presuming it's an 8 bit parallel DAC you simply need to connect it to a single 8 bit port on the PIC.

 

[tyron123]

ne way to inc current?

is there any way to inc the current comming out of the op amp? i am currently getting .3mA and 2V from the op amp , the op amp(LM 741) is hooked up from the DAC(0832). the op amp is hooked up as a voltage follower, i need at least 4mA , between 4mA to 16ma actaully..
i treid hooking it to a transistor NPN2222A but i got the same current out.

thnx any help is appreciated..
Tyron

 

[Nigel Goodwin]

Re: ne way to inc current?

is there any way to inc the current comming out of the op amp? i am currently getting .3mA and 2V from the op amp , the op amp(LM 741) is hooked up from the DAC(0832). the op amp is hooked up as a voltage follower, i need at least 4mA , between 4mA to 16ma actaully..
i treid hooking it to a transistor NPN2222A but i got the same current out.

I think you had better post your circuit, there should be no trouble getting the current you need.

 

[tyron123]

heres the digram...

thnx for the help guys..
jus need to find out a way to boost current.. to some where between 4mA n 16mA if i need to contol it.. i can probably use a pot later on

 

[Nigel Goodwin]

A quick google found the datasheet, which shows the opamp connected very differently?.

 

[tyron123]

i get less amp that way

yes i tried it that way? but i only got 0.136 mA... so i had to try it into a voltage follower.. its kinda werid.. coz i was expecting more from the op-amp... the data that the dac is reciving is 1111 1111. so a full fledged thing... isnt there some sorta transistor resistor circuit that can boost of the current? or act like some sorta buffer?

Tyron

 

[Nigel Goodwin]

Re: i get less amp that way

yes i tried it that way? but i only got 0.136 mA... so i had to try it into a voltage follower.. its kinda werid.. coz i was expecting more from the op-amp... the data that the dac is reciving is 1111 1111. so a full fledged thing... isnt there some sorta transistor resistor circuit that can boost of the current? or act like some sorta buffer?

I would suspect you have something wrong somewhere, the opamp is already a buffer - you shouldn't need to add anything else.

I'm also rather confused about 'only got 0.136mA', what are you actually trying to do?, and how (and why?) are you measuring the current?.

The circuit outputs a voltage, the digital number fed into the DAC produces a corresponding voltage at the output of the opamp.

 

[tyron123]

maybe the DAC is messed up?

i am not too sure.. that suprisees me as well.. but i mite have a feeling that the DAC mite be messed up..
iwill have to try with another one i guess.. but i cant do so until monday..
any idea what should be the value outta the opamp normally?
Tyron.

 

[tyron123]

measuring using a multimeter

the current and voltage i measure using a multimeter.. and voltage is supplied externally by a DC +/- 15 v
i forgot to metnion that before..
Tyron

 

[Nigel Goodwin]

Re: measuring using a multimeter

the current and voltage i measure using a multimeter.. and voltage is supplied externally by a DC +/- 15 v
i forgot to metnion that before..
Tyron

But how (and why?) are you actually measuring the current?, measuring the current is generally done to see how much power a load is taking, you've never mentioned what load you are using.

If you're simply sticking an ammeter from the output of the opamp to ground, you're shorting it out and it's not going to work.

 

[tyron123]

ok what do i do?

ok.. im a lil fuzzy on this now.. how do i measure the current comming out of the opamp..
i am not puttin in any load.
but i have a feeling i might have to put in a FET if i want to inc the current output.. but then again i mite be wrong since i might be measuring the current wrongly..
but i am open to recommendations..
Thnx
Tyron

 

[Nigel Goodwin]

Re: ok what do i do?

ok.. im a lil fuzzy on this now.. how do i measure the current comming out of the opamp..
i am not puttin in any load.

You need to measure the current into the load you're going to use - what is it supposed to feed?.

 

[tyron123]

feed a pump

the current is supposed to drive a pump that operates between 4ma and 16ma ....

 

[tyron123]

Re: ok what do i do?

was the site down a few days ago... thats y it took me long ot reply..

ne ways i tried a coupla different methods to amp the current such as current amp for opamp and transistor as a buffer and now we are using a FET (no avail) .the external power supply that i am using provied +- 20 and upto 0.5ma
that is fed into the DAC and op amp.
Tyron

 

[Nigel Goodwin]

Re: ok what do i do?

was the site down a few days ago... thats y it took me long ot reply..

Yes it was, but no explanation was ever given!.

ne ways i tried a coupla different methods to amp the current such as current amp for opamp and transistor as a buffer and now we are using a FET (no avail) .the external power supply that i am using provied +- 20 and upto 0.5ma
that is fed into the DAC and op amp.
Tyron

I'm somewhat bemused by the power supply you mentioned?, you said the pump requires between 4mA and 16mA - yet the power supply can only supply 0.5mA, how do you expect it to work?.

 

[tyron123]

ok so what do i do now? ne ideas?

if i change the external power supply to 6v i can get upto 2.5ma from it.. but i am guessing that would not be enough to drive the opamp and the DAC
thats was y i wanted some sorta current amplifier..
so umm.. what do u recommend i do? :?:
Tyron
:?

 

[Nigel Goodwin]

Re: ok so what do i do now? ne ideas?

if i change the external power supply to 6v i can get upto 2.5ma from it.. but i am guessing that would not be enough to drive the opamp and the DAC
thats was y i wanted some sorta current amplifier..
so umm.. what do u recommend i do? :?:
Tyron
:?

I suggest you post your complete circuit, including the power supply, the current capacity figures you keep mentioning from your power supplies don't make any sense.

 

[tyron123]

I"LL do that ASAP

due the lack of time and 4 running projects... gimme a lil while and i will post op the complete circuit...
i hope i get all those 4 projects done before the end of the semester..
Lates n Thnx
Tyron