Any idea's for a buffer?

[things]

Me and a friend are designing a lasershow controller consisting of a FTDI USB-serial chip and a DAC from Analog, but because the output of a PC is not always steady, we need somehting to buffer the serial data until a new chunk of data is received. Any idea's?

Cheers,
Dan

 

[Nigel Goodwin]

Use a PIC to do it, or any other micro-controller - you need to intrface the DAC in someway anyhow, presumably it doesn't just take RS232?.

 

[things]

Hmm OK, Thanks.. We are intending on using this DAC chip: AD5668 | Octal, 16-Bit D/A Converter with 5 ppm/°C On-Chip Reference in 16-Lead TSSOP | D/A Converters | Digital to Analog Converters | Analog Devices

-Dan

Hmm, why is my Reputation bad? I haven't done anything wrong have I?

 

[Pommie]

Me and a friend are designing a lasershow controller consisting of a FTDI USB-serial chip and a DAC from Analog, but because the output of a PC is not always steady, we need somehting to buffer the serial data until a new chunk of data is received. Any idea's?

Cheers,
Dan

There is no device that can buffer data that has not been received. A Pic will buffer the data until more data is required. You will require handshake lines or the Pic will get full up very quick.

Mike.

 

[Pommie]

Hmm, why is my Reputation bad? I haven't done anything wrong have I?

I don't know why people do that to new posters. I wish they wouldn't.

Mike.

 

[things]

There is no device that can buffer data that has not been received. A Pic will buffer the data until more data is required. You will require handshake lines or the Pic will get full up very quick.

Mike.

Sorry, I didn't mean to buffer invisible data, I meant to buffer the previously sent data untill new data is received.

-Dan

 

[Pommie]

Sorry, I didn't mean to buffer invisible data, I meant to buffer the previously sent data untill new data is received.

-Dan

I guessed as much and was just having a little fun.

Mike.

 

[things]

hahaha OK

Well, essentially, we have the FTDI drivers here for a premade DAC that uses a FTDI chip too, so essentially all we need to do, is interface PC ->FTDI USB - Serial -> Buffer -> DAC and then amp 2 of the DAC outputs to +/-5V differential, and the other channels to just 5-0v, then the rest is just software. Sounds about right, am I missing anything?

 

[Pommie]

What speed will the serial be running? Feeding what I assume is a stereo DAC at good quality is a lot of data and will define how you can solve the problem.

Mike.

 

[things]

What speed will the serial be running? Feeding what I assume is a stereo DAC at good quality is a lot of data and will define how you can solve the problem.

Mike.

Hi, the DAC chip I linked is 8 channels, 16bit. My friend reckons about 30mhz.

Essentially, we need to amp 2 of those output channels to give us +/-5v, or 10v PTP, and the other 6 are just going to be 0-5V output.

-Dan

 

[Pommie]

At that speed you need to look at one of the FTDI chips/modules with built in fifo. A pic is not a good choice.

Mike.

 

[Nigel Goodwin]

At that speed you need to look at one of the FTDI chips/modules with built in fifo. A pic is not a good choice.

That value sounds incredibly high, the original post was for a laser light display - you're not going to need anything terribly fast for that, and do you really need 16 bit?, would it give any advantage?.

 

[things]

The galvanometers can range all the way up to like 40,000 points per second, and we are aiming for just over 30,000 points per second, so it needs to be relatively fast. Using 16bit would mean better resolution, and many laser show controllers use 16bit.

 

[Hayato]

30,000 points per second = 40 kHz, not 30MHz.

You'll need something around 640 kHz or 1MHz but no more than 1MHz.

 

[things]

Makes Sense, thanks

So basically, we are going to interface FT2232C

to AD5668 | Octal, 16-Bit D/A Converter with 5 ppm/°C On-Chip Reference in 16-Lead TSSOP | D/A Converters | Digital to Analog Converters | Analog Devices

then just use opamps to amp the DAC output. Seem like it would work? We realize the USB-serial converter is a dual channel thing, but it has all the features we need, and cheap enough, so we are just going with it

Advice would be appreciated

-Dan

 

[Hayato]

Seems OK to me.

I suggest using this 16-bit ADC:
http://www.electro-tech-online.com/custompdfs/2009/04/AD5541_5542.pdf

It has 1 voltage output and you don't need to play with addresses and configuration bits.

IMHO I don't think you need 16 bits. You are going to filter the output, the laser cannon motor itself work as a filter.