DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

Jan Cumps — Sat, 04 Aug 2018 08:52:32 GMT

The HART experiment is finished. It works [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/6646.contentimage_5F00_1.png:16:16].

DAC8775 Quad-Channel DAC EVM - part 5: HART Interface

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

snidhi — Mon, 30 Jul 2018 10:10:45 GMT

Hi Jan,

You are doing great work. I am following your blog very closely.

I myself wanted to dive in the unique world of ADCs and DACs. By following your measurement techniques I kind of am getting the understanding of it. Keep going [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/5557.contentimage_5F00_1.png:16:16]

Cheers ;

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

michaelkellett — Mon, 30 Jul 2018 08:25:21 GMT

I've just bumped up the user rating - not that I pay them any attention.

This is the kind of stuff we want to see - I wish I had more time to do some more of my own.

I've not encountered HART before - seems like fun.

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

jw0752 — Sun, 29 Jul 2018 14:14:00 GMT

Hi Jan,

Posting about this type of experiment is very interesting and important for the forum. I always learn some new things from your blogs. What do the Stars know?

John

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

Jan Cumps — Sun, 29 Jul 2018 11:51:40 GMT

I got a user rating of one star on this post. My "flash a led" posts are more popular [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/contentimage_5F00_1.png:16:16].

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

Jan Cumps — Sun, 29 Jul 2018 11:33:09 GMT

The DAC8775 has a HART interface. You can modulate current output with a superimposed current, by providing an AC voltage of 500 mV pp at 1200 and 2200 Hz.

The signal has to be capacitively coupled.

The result is that the constant current output (here 6 mA) is modulated with a 500 µA component.

[View:/resized-image/__size/765x332/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/4745.contentimage_5F00_188073.png:765:332]

To enable this, you have to set the Enable HART bit in register 0x04.

[View:/resized-image/__size/759x431/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/7077.contentimage_5F00_188074.png:759:431]

The Evaluation Kit PCB will have to be modified, because all HART pins are by defult coupled to ground via a capacitor.

[View:/resized-image/__size/745x724/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/6472.contentimage_5F00_188075.png:745:724]

Here's the schematic for channel A:

[View:/resized-image/__size/703x369/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/1614.contentimage_5F00_188076.png:703:369]

On the PCB, I'll have to remove the C58 and induct the HART signal. This is an 0603 component. That's in the comfort zone.

[View:/resized-image/__size/753x638/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-4a1f2839-a169-4920-8918-15520f686dfe/3833.contentimage_5F00_188077.png:753:638]

This is a functionality that will translate well to an oscilloscope image, and the HART protocol is something that isn't discussed on the community that much.

Two good reasons to do the exercise.

RE: DAC8775 Quad-Channel DAC EVM - part 4: Current Mode

genebren — Mon, 23 Jul 2018 14:31:34 GMT

Another well documented experiment in your blog series on the DAC8775!

Gene