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6600gt
02-06-2007, 08:04 PM
I know some teams have successfully used them to interface to the OI before.

Can some one give provide me with some recommendations for some simple to program, cheap D/A converters?

This is going to be used to interface a custom circuit to the OI.

Thanks

EHaskins
02-06-2007, 09:15 PM
You might want to look at how team 862 interfaced a playstation controller. Their whitepaper (http://www.chiefdelphi.com/media/papers/1794) says what components they used.

You could also look at Microchip's digital pots (http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=11026&mid=11&lang=en&pageId=79).

I don't have any experience with the microchip parts, but I think they should work.

Jared Russell
02-06-2007, 11:25 PM
There are a variety of DACs that you can build using discrete ICs, or even just resistors. Google things like "R-2R" or "Weighted Resistor DAC".

All the same, I do suggest that you look into digital pots if they fit your application...it will save you some time.

Tom Bottiglieri
02-06-2007, 11:48 PM
AD looks like a good place to start.
http://www.analog.com/en/cat/0,2878,761,00.html

Tatsu
02-07-2007, 12:18 AM
Drop me a PM if you'd like. we just implemented a I2c->Analog sensor interface using the AD8652. It's a really easy to use R-2R dac which outputs the binary value from 1mv -> 4095 mV in 12 bits.

Also, if you have PIC programming capability, you could use a I2C / SPI dac and get better performance... not that it matters with the 8 bit OI ADC.

Chris Hibner
02-07-2007, 08:34 AM
It depends on how much resolution you need, but the easiest way to do an 8-bit D/A is to use a PWM channel and an RC filter. Just be sure the time constant of the filter is much larger than the period of the PWM signal. You can do a search on the internet to find examples of a PWM/RC D/A.

6600gt
02-07-2007, 09:52 PM
Thanks everyone.

I really don't have the time to develop much hardware(soldering up a whole string of registers). I want to use this system this year, and the deadline is approaching fast...

I do have access to PICs with SPI or I2C interface, in fact, that is what I intend to use. I would like to have a 4 channel output to be able to take advantage of one full port(able to send 4 bytes at a time)

I am looking at D/A converters because I need the full range. Its going to be used for data communications(analog port is the only legal way to get to the RC from the OI). Some one on one of the other threads said that digital pots have a +/- 30% resistance variability so...

I was looking at some Maxim DACs, and they seem like they would get the job done. Any specific suggestions on what types or features I should be looking for? I just need something that I can get going with fast!

Thanks

Jared Russell
02-07-2007, 11:16 PM
If you are indeed doing this on the OI, keep in mind that you are limited to a MAXIMUM of 100mA from the 4 joystick ports combined, and these are the only legal power sources for your OI components (the Chicklet is the exception to this rule).

That's going to mean that whatever you design has to be very low power.

6600gt
02-07-2007, 11:49 PM
If you are indeed doing this on the OI, keep in mind that you are limited to a MAXIMUM of 100mA from the 4 joystick ports combined, and these are the only legal power sources for your OI components (the Chicklet is the exception to this rule).

That's going to mean that whatever you design has to be very low power.

I thought it was 100mA per port! How much power does each individual joystick pull?

I am going to put an LCD on there without back lighting so it should only pull about 30mA and the PIC and MAX232 should pull about 20mA so I think it will work.:confused:

It will be sweet if it works though...

Tatsu
02-08-2007, 10:49 AM
Why not just use one of Analog's serial input quad DACs and bitbang the outputs? you could probably get a quad dac working faster that way than writing your own I2C stuff (unless you're already odne this, in which case its a moot point..)

6600gt
02-08-2007, 09:11 PM
Why not just use one of Analog's serial input quad DACs and bitbang the outputs? you could probably get a quad dac working faster that way than writing your own I2C stuff (unless you're already odne this, in which case its a moot point..)


Do you think this (http://www.analog.com/en/prod/0,,AD7304,00.html) will get the job done? Are there any special characteristics that I should be looking for?

Tatsu
02-08-2007, 10:27 PM
that looks good. SPI is a plus, as PICs have SPI support built in (usually).. 8 bit quads are good since the OI is 8 bit (last I remember anyway) what you picked seems ideal to me. PM me if you have any problems.