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I'm using the mcp4822 DAC and i'm very satisfied for controlling voltages in my circuits. But I wonder why the chip costs from 1 to 4 euro when a clone arduino costs around 3.50e.

Because I'm interested to control a great amount of signals (from 100 to 200) the price is too expensive. Are there any cheap alternatives? (i'm looking for at least 12 bit ic)

Frida Kahlo
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  • Volume is one of the keyfigures that drives prices up or down. – PlasmaHH May 24 '17 at 12:00
  • You could use 74HC595 shift registers and a bunch of resistors. They are 8 bit, but can be stacked to whatever you need. Also as you pointed out you could use a simple and cheap MCU with more pins and resistors. It would be better than shift register as you may implement the comunication protocol as you like it. Talking about a 12-bit precision however pulls you back to DACs as they will be much more precise than other solutions. – Todor Simeonov May 24 '17 at 12:19
  • Find a MCU with many pulse-width-modulator outputs; filter each PWM at 10hz or 100Hz or 1,000Hz to remove most of the rail-rail energy. You'll use the average to provide your output signal. – analogsystemsrf May 24 '17 at 12:39
  • @FridaKahlo DACs, aside from audio types, are not that common in high volume products. Some expensive MCUs have (mediocre- eg. 12-bit) DACs built in, but many applications that need a DAC can either use PWM or require a 16 bit or better DAC. Maybe you should control your signals in the digital domain rather than trying to use such low-end parts. – Spehro Pefhany May 24 '17 at 13:22
  • @FridaKahlo: for each person wantnig to buy a dac, you find hundreds wanting to buy a failduno – PlasmaHH May 24 '17 at 13:25
  • @FridaKahlo: a DAC is not a golden hammer, you can't solve every problem with it, in fact only a minority of things people do with their tinkermakertools might benefit from a dac. you dont need one to drive motors. or read sensor data. or communicate. or make lights blink. – PlasmaHH May 24 '17 at 13:59
  • "design once and you print for ever" - yes, but it's quite a big investment in design, very few commercial chips cost less than $1m once you add up staff and software licensing costs. It seems that most applications are happy with "one bit" PWM or delta-sigma systems. What bandwidth do you want out of your DAC system? Why is filtered PWM deemed inadequate? – pjc50 May 24 '17 at 14:00
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    Solenoids are basically inductors so PWM (with a catch diode) works just fine, V=L * di/dt and all that. DACs are useful, but ALL engineering is a compromise, you pick the technology that best meets you price/performance trade off for each application. Incidentally a two channel audio DAC with around 16 bits ENOB is less then £1 in quantity 100 if you pick the right part, the interface is a little tricky for most micros however (Delta sigma parts need a continuous clock). – Dan Mills May 24 '17 at 14:28
  • @FridaKahlo: Do you suggest to make computers communicate in music just to be able to use dacs? also where in reading sensor data is a dac useful? solenoids are on or off, use a transistor, not a dac. dacs have their uses, its just that they are not useful everywhere and that just a normal microcontroller has much more applications than DACs. – PlasmaHH May 24 '17 at 14:29
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    @FridaKahlo: nope, the prices won't drop. People will not suddenly use DACs more in fields where they did not before. The amount of applications for DACs is just orders of magnitudes less than for µCs. You might need a µC for almost every application you run a DAC in, but you don't need a DAC for the majority of applications you use a µC for. Just like people drive cars and not buses, although a bus can accommodate much more passengers, for that moment where you might need it. You seem to have a narrow view of what people do with electronics. Just look around what is running with µCs w/o DACs. – PlasmaHH May 24 '17 at 14:39
  • A delta sigma modulator is not that hard in software, and for things as slow as solenoid drivers is perfectly adequate, you really don't want analog here, it begets heat in your drive amplifier transistors, which PWM of either kind does not to anything like the same degree. The major use for DACs outside of audio is for things like automatic calibration of other analogue parts, nobody uses them for conventional solenoid drivers unless they are running ultra fast things at nearly audio rates, and even then PWM with hardware support is common. – Dan Mills May 24 '17 at 14:41
  • If you're using one of the popular class D amplifiers, there isn't a DAC at the end of the audio chain, just high-frequency PWM all the way down. – pjc50 May 24 '17 at 14:42

1 Answers1

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Analog is expensive, by and large, and a 12 bit part (if it actually does manage 12 bits) is actually a surprisingly high precision component (1 part in 4096, it is probably laser trimmed), and due to process issues both requires processing different to that used for digital stuff and in ways that tend to be fab specific.

A relatively simple microcontroller on a not very fine mask geometry (Those things are very far from state of the art) is the sort of thing that any random cmos fab can probably run, and it does not need laser trimming (Takes time per component).

Now depending on what update rate and precision you need the obvious thought is to use one DAC, some analogue switches and caps, maybe plus some opamps to drive multiple outputs, for example you could use a 74HC4067 plus 16 small caps to drive 16 high impedance signals from 1 DAC, time division multiplexing the updates and holding the voltage on the caps between updates.

Volume also matters a lot, look at pricing when you buy whole reels of parts (and not from Mouser either), rule of thumb is that the full service distributors (Mouser/Digikey/Farnell/RS and the like) mark up by about 100% or so for the convenience, if you buy in quantities sufficient to interest the field sales guys you tend to get MUCH better pricing.

Needless to say the guys making cheap ass arduino clones are buying multiple reels of parts at once and are not shopping at Digikey, they will also likely accept a rather higher part failure rate which can again make things cheaper if you are prepared to shop grey market in Shenzen.

Dan Mills
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  • Interesting. Thanks. The circuit you describe is a "sample" and hold circuit? So you say that the prices are justified? It is like precision amplifiers? And why "laser trimming" is so difficult? Isn't an automated process and couldn't be applied on the whole die? – Frida Kahlo May 24 '17 at 13:12
  • It is automated, but it has to be applied to each die individually - which adds pennies at the factory which get multiplied up by the margins of distributors along the way. – pjc50 May 24 '17 at 13:57