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+=========================
+ ZPB30A1 Electronic Load
+=========================
+
+:Author: David Douard
+:Category: Electronics
+:Tags: ZPB30A1, electronic load, test equipment
+
+A few weeks ago, I purchased a cheap electronic load from AliExpress
+(`this one`_ to be precise). It's a ZHIYU model ZPB30A1. It's
+specifications are:
+
+- constant current mode 
+- max voltage: 30V
+- discharge current: 0.2A to 9.99A (+/- 0.7% + 1 digit)
+- max dissipated power: 60W
+- voltage measurement error: 1% + 2 digits
+
+It supports 2 operation modes:
+
+- electronic load: in this mode, you can set the current and the
+  minimum voltage above which it beeps; in this mode, it display the
+  measured voltage and set current.
+- battery capacity test mode: in this mode, you set the discharge
+  current and the lower voltage limit at which the discharge test
+  stops. It displays the total discharged capacitu (in Ah) and energy
+  (in Wh).
+
+.. image:: {filename}images/ZPB30A1/zpb30a1.jpg
+   :alt: Overall view of the ZPB30A1 electronic load
+  
+The device looks pretty nice and reasonably well built. It can do 4
+wire measurements.
+
+The device itself is built around a single ST W60N10 N channel MOS
+transistor (100V, 60A, 200W) and a STM8S005K6 microcontroller.
+
+.. image:: {filename}images/ZPB30A1/zpb30a1_board.jpg
+   :alt: Main PCB of the ZPB30A1 electronic load
+
+The shunt resistor is a 10mΩ wire. A very small value that explains
+the rather big minimal current of 200mA (which means a voltage drop as
+low as 2mV).
+
+.. image:: {filename}images/ZPB30A1/zpb30a1_mosfet.jpg
+   :alt: Main transistor of the ZPB30A1 electronic load
+
+One nice thing with this device is the fact that every component value
+is written on the PCB: no need to use the magnifier to read the SMD
+parts values.
+
+The bottom side of the PCB is pretty empty besides the ground plane.
+
+.. image:: {filename}images/ZPB30A1/zpb30a1_bottom.jpg
+   :alt: Bottom side of the PCB of the ZPB30A1 electronic load
+
+
+The most annoying thing is the minimum current of 200mA, which pretty
+hight. It's obviously not designed for small battery or PSU
+testing.
+
+Another thing is that its limited to CC mode only (does not provide
+constant resistance mode nor constant voltage). It's a bit unfortunate
+since it's probably only a matter of software.
+
+Also, the usability is quite rough. For example, to choose the
+operating mode (between CC charge and battery capacity test mode), you
+have to power off the device and power it on holding the start/stop
+button down.
+
+The last missing feature, for me, is that there is not "output" port
+allowing to capture the values when doing a battery discharge
+test. The good news is that there is unpopulated port. Looks like some
+ISP/serial port directly connected to the microcontroller.  Pins are
+labelled as G, R, T, L, F and Vc. G stands for ground, and Vc is
+obvious.  R and T might be Rx and Tx of a serial port. F and L are not
+obvious.
+
+So I've probed a bit to see if there are any signals.
+
+The overall (messy) setup was:
+
+.. image:: {filename}images/ZPB30A1/overall_setup.jpg
+   :alt: Overall testing setup for the ZPB30A1.
+
+During this test, the electronic load was sunking almost 1A at 30V,
+thus dissipating around 30W. The MOSFET transistor was getting a bit
+hot. I measured 65°C with my cheap IR thermometer.
+
+The F pin shows a square signal at 50kHz, and there is some activity on
+the T pin. I've used my new Rigol DS1054Z scope to try to find out if
+the signal is meaningful. And after playing a bit with the Serial
+decoder, I finally found that:
+
+.. image:: {filename}images/ZPB30A1/DS1Z_serial.png
+   :alt: Serial signal on the T pin.
+
+When the ZPB30A1 was actually set up like this:
+	
+.. image:: {filename}images/ZPB30A1/zpb30a1_setup.jpg
+   :alt: Testing setup for the ZPB30A1.
+
+So the measured voltage is constantly written on the serial port at
+115200 baud, 8N1. The third value is 1 when it is normally operating,
+and 0 when the voltage is below the limit.
+
+However, in battery discharge mode, there is nothing on the serial
+line.
+
+Now, I have to solder a socket in there. Then the next step will be to
+see if we can send commands to the ZPB30A1. I may need to learn a bit
+about the ST microcontroller...
+
+
+
+.. _`this one`: http://fr.aliexpress.com/item/New-Constant-current-electronic-load-9-99A-60W-1-30V-battery-capacity-teste-free-ship/32571919265.html
+
+