Digital to Analog converter

**hansika** · 08-05-10, 06:29

Hi friends,
i need to connect five 12 bit DAC to a microcontroller(8051) and my requirement is i need to activate only one DAC at a time by the microcontroller, so please suggest me how to connect 5 DAC to 8051 microcontroller and is there any way to activate them one at a time,please suggest me a DAC which will meet this requirement

**keith1200rs** · 08-05-10, 07:17

You could use 1 DAC and 5 sample and holds.

Keith

**hansika** · 08-05-10, 08:03

can you please explain me how it going to operate, my five DACs output will going to 5 signal conditioning modules, so how can i connect one DAC with sample and hold circuits with signal conditioning modules, i am newbie to micro controller please explain me,thanks in advance

**bobcat1** · 08-05-10, 09:47

Hi

Just use an ADC with a multiplexer - search TI site for Digital to analog converter

All the best

Bobi

The microcontroller specialist

**keith1200rs** · 08-05-10, 11:13

It is a DAC not an ADC that is required, so it needs 5 sample and holds not a multiplexer, although I guess you could view 5 sample and holds as a form of multiplexer.

Keith

**karesz** · 08-05-10, 11:57

Hey all,
Im sorry, but I would unsure!

...
Hansika wishes to control 5 DACs from a 8051, also it means not a need of S&Hs, but more out put latches or latched input DACs with a 5x control lines( a 3 to 8 decoder i.e.)...
That is to call unusually as S/H, but its not, its a data-latch/register or data demultiplexer (in my opinion).
Greetings!
K.

**keith1200rs** · 08-05-10, 12:27

I was just suggesting a single DAC with 5 S/H as an alternative to 5 DACs.

Keith.

**karesz** · 08-05-10, 12:42

Yes Keith,
I did understand it_ maybe have not perfectly wrote, but I spoke over 5 control lines too, as same circuit proposal.
I have only problems with the given name of "sample & hold", because for my understanding is S&H for analog circuit & these one is to call as latch or register (for the uC`s (i.e. 8 bit wide) data output ...
K.

**srizbf** · 08-05-10, 19:38

if this is what you require:(as i understand)

you have 5 dacs and 8051(one) (:

since each is 12bit you can connect P1 and any other unuse port 4bits(say P3)
(depends on your application) all together.

if each dac have a select or strobe/latch line , connect each one to
one portbit each of othe unused port.(say P0 bit no 0to4).
also select appropriately the \wr control line , if any.

select through program each dac one(of strobe/latch line) by one and output 12bit word to it.

as simple if my understanding is correct.

srizbf
8thmay2010

**hansika** · 15-05-10, 06:05

i found a DAC with part number AD7545ACQ-ND. it is having one chip select and write pin but i dont understand what is vref pin in that ic can anyone please susggest me whether that my controller will suitable for my application or not

**karesz** · 15-05-10, 12:13

Hi,
Your DAC must have a CLEAN voltage (yet called URef.) to divide it into your bits(in that case 4K steps)...
Of course you can select some converters with "on Chip" ref source too, but it needs every time a voltage source (in worst case simple the +Usupply; as i.e. by PIC solutions).
I can not see some problem with it for your project...
K.

**BurnOut_tesla** · 15-05-10, 12:56

Hey hi hansika...
can u tell us which microcontroller ur using...
r u using controller with in built ADC..???

**BurnOut_tesla** · 17-05-10, 06:24

Hey hansika,
I dont think u need sample and hold circuit..
If ur directly connecting AD7545 output to pic then u dont need multiplexer also
coz 30Fxx has more than ADC (16 channel)
If u want to signal conditioning circuit then feed outputof each AD7545 to 4051,
then switch according to ur requrement using A B C select line and feed output od 4051 to signal conditioning
and give output of signal conditioner to ADC of PIC..
as ur switching the channel by A B C u know which channel ur facing..
ultimately ur using only one ADC of ur controller.....

Added after 1 minutes:

By the way what r u interfacing with AD7545??
from where this digital data is cuming..??

**srizbf** · 17-05-10, 07:20

the op wanted dac suggestion for 8051 .
not pic

srizbf
17thmay2010

**BurnOut_tesla** · 17-05-10, 07:31

she is using dsPIC not the 8051...
she has told me that...

**hansika** · 17-05-10, 11:25

Thanks for your suggestion but i am connecting output of dspic(digital data) to AD7545 to convert it to analog value, if it will solve with 8051 micro controller then it is very helpful for me because i am familiar with 8051 programming compare to pic programming.

**BurnOut_tesla** · 17-05-10, 11:29

can u tell me ur application oe schematic..??

**hansika** · 17-05-10, 12:10

It is not a big application i want to learn micro controller programming, how different types of peripherals interfaced with micro controller.if i want to interface multiple ADC and DACs to micro controller say suppose if i want to interface AD7545 with micro controller it will take 12 pins for each DAC if i use 3 DACs then it will take 36 pins, i want to avoid this high no.of pin requirement with multiple DACs so i need suggestions how it will done with less no of pins.