Precision Current and Voltage Signal Generator

A while back, I picked up this voltage and current reference from AliExpress. It has a product number, I think of ZYX-HOD-2AO-VI, but who knows? I can't remember which person had mentioned it to me, but they thought it had excellent characteristics, and behavior far in excess of what you might expect for a sub $15.00 device. It's also quite compact at 3.9" (100mm) by 2.36" (60mm) by 1" (25mm).

One thing it didn't have, though, was a good manual, so I've pulled this together from both it's kinda "manual", some digging, probing, and general beating my head against the wall.

Let's start with the specs:

The one I bought has a built-in 3.6V LiIon battery that can be charged over a micro-USB connector. The screw terminal lock is also removable, something they don't typically mention. This means you can potentially swap them quickly for various setups.

Inside the Box

As I mentioned above, this device is far more complicated than anything at this price point has a right to be. If you pop the front cover off after removing the rotary knob, you peer inside, and find this.

That's a lot for what this does. Unfortunately, they've scrubbed all the ICs of any marks. There's one inside that has the faint residual marking of "ZYX", but that's useless. There's a few seemingly high-quality polyester caps as well (marked 334J100 on top). Still, impressive for the price, and explains the rather outstanding performance.

We truly live in a bizarre, and in many ways golden, era of electronics.

Power Options

There are three ways to power the one I have:

1. External 15-30VDC power supply, which it will never draw more than 1W operating, and 5W charging.
2. External micro-USB at 5V and 0.2A operating and 1A charging.
3. Internal 3.7V battery.

Obviously, you can only use one of these at a time.

Output Modes

There are two output modes, current and voltage, which you can think of a constant-current and constant-voltage sources. You can switch between them using the MODE button.

Terminal Block

On the top of the device, there is a (removable) screw terminal bock. It has 6 connections, which are numbered left to right 1-6:

Changing Parameters

Getting to the parameters setting is a bit weird. First, there are settings for each mode (voltage v current), so you will need to make sure you're in the right mode before starting. To get access:

1. Press and hold down the control knob for 2 seconds. This will display F001, which is a reference to parameter 001.
2. Rotate the knob clockwise to select F002. The first time you do this, you will get a display consisting of 4 underlines: _ _ _ _. This means that the device wants a passcode.
3. To enter the password you rotate the knob clockwise for a |- symbol or counterclockwise for a -. To get to parameters F002-F009, you use the passcode |- - - |-. That's clockwise, counter-clockwise, counter-clockwise, clockwise. Then press down on the rotary control. To get to F100-F109, you will use a different passcode, which is |- - |- -, or clockwise, counter-clockwise, clockwise, and counter-clockwise. Again, press down on the rotary control.
4. Rotate the the parameter you want to change, then press down on the knob.

After you've set a parameter, or once you've not interacted with it for 10 seconds, it will return to "normal" operation.

Quick Output Mode

It is possible to set "preset" voltage and current settings, but no matter what I try, I cannot figure out how to access them after they have been set. If you know, please let me know!

Adjustment Steps

Out-of-the-box, the unit does voltage steps in 0.1V increments, and current in 0.1mA steps. This can be adjusted using the parameters F004 and F005 mentioned above. For both, the coarse adjustment steps controls how many tenths (0.10) each click of the rotary knob increases things. I have yet to figure out how F005 works, actually. It seems to imply that it might be adjusting at the hundredths, but that just doesn't seem to be the case.

Saving Values

If you want to set a "default" value for it to start up in, you can short-press the rotary wheel (about 1s). When you do that, it will display . . . . on the screen, which means it saved the value. Now, when you turn the box back on, it will use that as the starting point.

Precision

I took the following measurements with a B&K Precision 2709B multimeter, but it should be good enough for hobbyist uses. Here's a few checks at a few points out-of-the-box, and before any calibration was done. I didn't do calibration as I don't currently own anything I trust more.

Calibration can be done using F007 and F008 in both current and voltage mode.

Mechanism of Operation

Honestly, not being able to see the labels on the chips makes it super hard to figure out how this thing works. Reverse engineering hardware isn't my expertise. But from reading a bit between the lines, I'm pretty sure it's a DAC-controlled constant voltage and current source. You can read more about how this might work. This would also explain why the current delivery is so low. Given the apparent 0.01V and 0.01mA precision, I would guess that it's driving it with a 12-bit DAC, which are relatively inexpensive at this point (under $1.00 in any quantity).