8 bit dac recommendation

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retepsnikrep

Senior Member
I'm after a part recommendation from the collective mind on here.

8 bit DAC.
8 pin dil package
5v supply and rail to rail output.
As much output current as i can get.

I2C or some sort of picaxe compatible serial interface.
Low cost.

Any thoughts and or examples with code used to drive it?

Thanks
 
W

westaust55

Moderator
MCP4725 i2c DAC but it is SMD package

TC1321 i2c 10 bit DAC but it is SMD package

MCP4822 (12 bit) / MCP4921 / MCP4922 DIL package but SPI interface

maybe have a read here as well:

http://www.picaxeforum.co.uk/showthread.php?t=14686

You may need to consider an Op-Amp follower if you want additional current capability.
Current through the DAC itself raises the chip temperature and can increase accuracy errors.
 
M

matherp

Senior Member
8 pin PDIP limits you but in order of price as RS look at TLC5615 (SPI), MCP4822 ( SPI), or MAX517 (i2c). For the TLC5615 code something like the fragment below (I think originated from hippy) should work but check the bit and byte order to match the chip
Code: 
	low CS
	tmp = highbyte
	FOR bitNumber = 0 TO 7
		b0 = tmp AND $80 MAX 1
		if b0=1 then:high SDO: else : low SDO:endif
		high SCK
		low SCK
		tmp = tmp * 2
	NEXT
	tmp = lowbyte
	FOR bitNumber = 0 TO 7
		b0 = tmp AND $80 MAX 1
		if b0=1 then:high SDO: else : low SDO:endif
		high SCK
		low SCK
		tmp = tmp * 2
	NEXT
	high CS
 
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techElder

techElder

Well-known member
As was just said by reference ... use the 18M2. DAC is built in.

DAC and FVR
  • The M2 parts support a digital-to-analogue converter (DAC) for accuate analogue voltage output.
  • The range of the DAC can be the supply voltage or a reference voltage generated by the Fixed Voltage Reference (FVR) module.
  • This module can be set to generate an accurate 1.024, 2.048, or 4.096V reference.
  • See: dacsetup, daclevel, readdac, fvrsetup
 
fernando_g

fernando_g

Senior Member
Limiting yourself to DIP8 packages, will limit you to a narrow selection, as most new semiconductor devices only come in SMT, and some companies are dropping out thru hole packages completely, even for "older' chips.

If you find a chip you like, but it is only available in SMT, you can always use an adaptor, availble from many sources. Mind you, some of those adapters even have space for some passive components (like decoupling caps), which means that you get excellent decoupling and very clean outputs.
 
R

retepsnikrep

Senior Member
Thanks for all the advice. I'll have a good look at it all. :)

Which 8 pin smt to dip adapter/supplier do people use then?

I can prototype it on my breadboard, but I need a wider board with more holes each side of chip. Most i have seen only have 4-6 holes per side?
 
W

westaust55

Moderator
I concur that using SOIC package Devices is relatively easy.
I bought 50 x 8pin SOIC to DIP adapter board from EBay some time ago and other than a magnifying glass to check position use through hole tools for these SOIC packages.

Also don't restrict yourself to 8 bit resolution. If you buy a 10 bit part, then you can always ignore the lowest two bits of data.
 
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womai

Senior Member
MCP4822 is a good DAC. I use it all the time. 12 bits but you are free to always set the lower 4 bits to zero. Note that its outputs can only go up to 4.096V (with gain=2), not 5V, but that's easy to correct by adding an op-amp stage with gain of approx. 5/4. MCP6021/22/24 are good models (have rail-to-rail inputs and outputs.
 
B

BeanieBots

Moderator
Anything wrong with PWMout into an RC and buffered with an op-amp?

Any DAC will require buffering anyway if you want current out of it and PWMout offers 10-bit resolution. The only downside is a slightly sluggish response due to the RC but you'll not be producing 10kHz sinewaves with PICAXE basic anyway so I doubt that would be an issue either.
 
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