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UART to parallel receiver(converter)

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avi

New Member
Hi all,
I'm looking for an IC or other easy solution to connect USART Receiver directly to a ADC?
I've made some search for a ADC with a USART interface, and I haven't found nothing.
so, I'm looking for a "stand alone" IC that will function as a USART receiver and has a parallel data out (that will be connected to a regular DAC).
TIA.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The cheapest and easiest method would be to use a PIC, and it would be a pretty simple programming task - just read the incoming serial data, and stick it on an output port feeding the DAC. One small 14 or 18 pin chip, one resistor for the serial interface, and that's all.

Alternatively you could use an old (VERY old) UART chip, these are usually the 6402, it's a 40 pin chip, and you need to provide a number of support devices around it, including a suitable oscillator for the baud rate you require.
 

gramo

New Member
You could have the PIC do the DAC work too, I did this up a while ago;



even though PIC's don't have a DAC on board to toy with, this method uses the Pulse Width Modulation module.

Here's a real life result of a CRO connected to the output of the above circuit. Note the Yellow channel is the raw PWM signal, and the Blue channel is the filtered DAC output;



Combining this with USART, like nigel said, would be a pretty simple programming task

http://digital-diy.com/micro/site/i...rsion-dac-via-pwm&catid=6:swordfish&Itemid=51
 
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avi

New Member
Of course, I take the easy way using PIC. I've written something and It seems to work well .
By the way, Gramo, Nice idea, but I need an accurate d/a conversion (for audio), so I think that using PWM will distort the signal.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Of course, I take the easy way using PIC. I've written something and It seems to work well .
By the way, Gramo, Nice idea, but I need an accurate d/a conversion (for audio), so I think that using PWM will distort the signal.
Not at all, except you're limited by how fast the PWM can be run at higher resolutions. But PWM D2A is just as accurate as a conventional one.

It really depends though how fast you're trying to run, and a USART interface tends to limit things anyway.

You might consider a simple R2R ladder DAC, as with whatever type you use you will need a low-pass filter after it anyway, and that can provide the buffer for the R2R.
 

gramo

New Member
Of course, I take the easy way using PIC. I've written something and It seems to work well .
By the way, Gramo, Nice idea, but I need an accurate d/a conversion (for audio), so I think that using PWM will distort the signal.
That it will. I tested the worst case scenario of a full scale deflection from 0% to 100% duty;



As you can see above, it takes 1200uS (1.2mS) to ramp from 0V to 5V. This is a fall back of the RC circuit as the capacitive time constant needs to be taken into account

Good for your everyday DAC output, but audio will need much a faster response.

On another note, I have used the MCP4822 with decent results.

Rail to rail output
Single Supply
Single/Dual channel
Short Circuit current 15mA Typ, 24mA max

You'll need a power opamp to drive a load of any size though.
 
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gramo

New Member
Not at all, except you're limited by how fast the PWM can be run at higher resolutions. But PWM D2A is just as accurate as a conventional one.
I might have got the above wrong, I'm sure nigel can clarify it :eek: I was thinking along the lines of a 1.2mS slew in full deflection would would reduce the max frequency well below 1/0.0012 (833Hz)
 

avi

New Member
MCP3002 is an ADC, and I need a DAC.. or I miss som.

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That it will. I tested the worst case scenario of a full scale deflection from 0% to 100% duty;



As you can see above, it takes 1200uS (1.2mS) to ramp from 0V to 5V. This is a fall back of the RC circuit as the capacitive time constant needs to be taken into account

Good for your everyday DAC output, but audio will need much a faster response.

On another note, I have used the MCP3002 with decent results. Single supply operation: 2.7V - 5.5V, SPI serial interface, and 200 ksps max sampling rate at VDD = 5V.

You'll need a power opamp to drive a load of any size though.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I might have got the above wrong, I'm sure nigel can clarify it :eek: I was thinking along the lines of a 1.2mS slew in full deflection would would reduce the max frequency well below 1/0.0012 (833Hz)
I don't think in those terms :D

Assuming he wants 20KHz audio bandwidth, he could do with running the PWM at 100KHz (if it will), but a minimum of 44KHz - with a very steep 20KHz active filter on it's output. If you can manage 100KHz PWM, then the filter doesn't need to be as steep.

However, as he's transferring data via UART, it's probably not that fast?.
 
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