A Remote Control Class For QJE3005P Like PSUs

Summary

QJ3005P is a remote control interface class for bench power supplies that have a couple of remote control capabilities, like QuatPower LN-3005P, QJE QJ-3005P, TEK3005P, Vellemann LABPS3005N etc. There are a lot of very similar devices available, apparently from the same chinese manufacturer, all sharing the same look and feel, and more or less the same remote control capabilities.

The xy3005P provides one adjustable PSU channel and can be controlled via USB serial emulation, at 9600 bps.

The remote control capabilities are limited and have some special properties that must be taken in account when using the interface class.

Supported PSU Commands

Command	Usage
*IDN?	Query for the PSU model name and product version
STATUS?	Query PSU mode of operation (C.V./C.C.) and output status (on/off)
VOUT1?	Query current output voltage reading
IOUT1?	Query current output current reading
VSET1:vv.vv	Set new output voltage to 0.0 ... 30.00 volt in 10 milli volt steps
VSET1?	Read the last maximum output voltage set point
ISET1:c.ccc	Set new output voltage to 0.0 ... 5.000 ampere in 1 milli amp steps
ISET1?	Read the last maximum output current set point
OUTPUT1	Load switch set to on (i.e. output enabled)
OUTPUT0	Load switch set to off (i.e. output disabled)

The QJ3005P API

Create a new instance of the PSU interface.

from psu.QJ3005P import PSU

qj3005p = PSU('/dev/yourtty')

Recommended: Use a with clause to interact with the PSU.

with qj3005p as psu:
    psu.set(volt=5, amps=.5)
    psu.enable()
    psu.read()

The API consists of several methods to query the PSU model/brand/version and operational status, to set voltage and current, to control the load switch, and to read current voltage and current readings back from the PSU.

API	Type	Remark
`psu = PSU('COMx')`	construct	create new control object and bind to TTY
`psu.open()`	method	start serial communication to device
`psu.close()`	method	stop serial communication to device
`psu.set(volt, amps)`	method	set new maximum voltage and current
`psu.get()`	method	read current and voltage, together with CV/CC and output status. Returns a tuple.
`psu.volt`	property	get current voltage reading from device, or assign new set point
`psu.amps`	property	get current ampere reading from device, or assign new amperes set point
`psu.enable()`	method	enable PSU output (i.e. load switch on)
`psu.disable()`	method	disable PSU output (i.e. load switch off)
`psu.status`	property	get current PSU output status and CV/CC status as a list of strings
`psu.name`	property	get the brand, name and hardware/firmware version of the PSU
`psu.is_availabl()`	method	query for availability of a PSU on the TTY
`psu_is_open()`	method	query for the TTY channel to be opened
`psu.is_enabled`	property	query the PSU for the current output status
`psu.mode`	property	query the PSU if it is currently running in CV or CC mode

Limits Of The PSU Hardware And Firmware

During remote control, the front panel knob and buttons are disabled.
Remote control mode can only be left by power-cycling the device.
OCP, memory recall and store settings is not possible with remote control. Works only by using the front panel. Preset OCP can not be influenced by remote control.
Voltage and current set points can not be read back without setting it first.
Awkward command delimiter: it is not CD LF or LF, but literally backslash+r backslash+n, or backslash+n alone.
Switching the output on or off needs some time to let the meter settle. Some wait time between switching the output and reading back the actual voltage and current seems to be recommendable.
Settings from remote can not be stored permanently on the PSU and do not survive a power cycle of the PSU.
The baud rate of the PSU serial channel is 9600 bps, as the user manual specifies. This is actually the default for new pyserial Serial objects, and this setting is implicit. The pyserial user manual does recommend setting a timeout for the PSU communication. Refer to the __init__ for details.
There is no clear error feedback from the PSU. Errors must be derived from status/ID feedbacks and voltage/current readings.

About The Code

The code was developed and tested with python 3.7 and python 3.8. May also run with earlier or subsequent versions of python.

Code was developed and tested on Windows 10, and tested on Raspberry Pi 4 and Raspbian. May also run on other platforms, that are supported by pyserial.

It comes with some examples and demos, how the interface class is intended to be used.