Monthly Archives: June 2015

PWM5 Complete Circuit Diagram

PWM5-CircuitThis is the complete circuit diagram of the PWM5 Solar Charge Controller. Click the image for the full size drawing.

The solar panel (max 100W) connects to the anode of the 90SQ035 Schottky diode at the top right of the drawing. The positive connection of the 12V lead-acid battery connects to Vbatt – Note that Vbatt appears in two different locations on the drawing and 0v (zero volts) in a number of positions along the bottom. Vgate is is the high voltage generated by the charge pump.


Fixing the JYE Tech DSO138 Oscilloscope

Click to enlargeAfternoon all!

I need to lift the 320×240 LCD display away from the main PCB, but have it still connected, so that I can fault find the negative supply for the analogue circuitry.

I came up with the idea of using an old IDE cable which has two sockets each with 2 rows of 20 pins on a length of ribbon cable. Unfortunately, the sockets have a missing pin presumably to prevent connection the wrong way round. Fortunately, the missing pin is not required by the LCD (as long as you connect it the right way round). So I’m drilling a small hole in the plastic.

Hmm, the IDE cable idea doesn’t work :(

It doesn’t matter how I orientate the ribbon cable, the pins don’t line up correctly.

IMG_20150612_151902[1]So on to plan B. I’m using a length of double row, long pin headers and lots of short female-to-female dupont wires to connect up all the relevant connections between the LCD and the main PCB.

Double check everything and apply power. The CPU seems happy (a double flash of the green LED). The LCD is still blank though.

IMG_20150612_152724[1]VGEN is present, a square wave of about 20% mark/space at 17.58kHz as indicated by my OWON oscilloscope. AV- is still 0.6 volts.

NPN transistor Q2 (9014) is looking suspicious – there’s a pulse train going into it’s base, but nothing on it’s collector.

Going to replace it with a 2N3904 which has the same pin arrangement. Part replaced, but no improvement.

IMG_20150612_161218[1]Some people have said that the inductor L2 has been a problem. Dig out my component tester and give it a test.

The component tester says it’s fine – 1.06mH with a resistance of 4.5 ohms.

Next, I’m not liking Q1, the PNP 8550 transistor. But it seems it’s OK too.

UNBELIEVABLE!! – These stupid 4-band resistors have ambiguous values. 120 ohms (brown, red, black, black, brown) is the reverse of 10k (brown, black, black, red, brown). I’ve swapped R12 with R37 and also R13 with R39. Now I REALLY HATE 4-band resistors :(

So with the resistors in their proper places, I now have -5 volts on the AV- test point. I also have a 2N3904 in place of the 9014 and a 2N3906 in place of the 8550, both appear to be good substitutions.

The user guide does suggest that all resistors are measured before putting them into the circuit, but it doesn’t mention that 120 ohms and 10k are the SAME COLOUR CODE!! Ridiculous.

IMG_20150612_171657[1]So, I now have all the proper voltages on the AV-, AV+, +3.3V and +5V test points, but the display is STILL BLANK!

Back to Banggood to ask for a replacement LCD.



Frequently Asked Questions

Q: What’s the value of the capacitors you’re using? – A: The two load capacitors connected to the crystal are both 20pF or 22pF. The capacitor in the reset line is 100nF.

Q: What value resistor did you use on the LED? – A: I used a 470 ohm resistor, but any value between about 220 ohm and 1k should work fine.

Power Bank Capacity Tests

YZXredI’m starting a project to test the capacity of a number of power banks, using the YZXstudio Power Monitors supplied by Franky Tong.

I’ll measure the charge (in mAh) required to fully charge the pack and the total charge recovered from the pack during discharge.

The test conditions are as follows:

  • Charge supply device:
  • Discharge device: Asus/Google Nexus 7 tablet (draws about 420mA)
  • Charge monitor: YZXstudio USB3.0 Power Monitor (yellow)
  • Discharge monitor: YZXstudio USB3.0 Power Monitor (red)


Avantek 20,000mAh External Battery Pack

  • Supplied input charge – 19,338mAh (previously 20,185)
  • Recovered output charge (5V) – 13,176mAh
  • Efficiency of boost electronics – 92%

EC Technology 22,400mAh Power Bank

  • Supplied input charge – 21,467mAh (previously 21,265)
  • Recovered output charge (5V) – 13,935mAh
  • Efficiency of boost electronics – 88%

PowerAdd Pilot X7 20,000mAh Power Bank

  • Supplied input charge – 20,092mAh (previously 19,964)
  • Recovered output charge (5V) – 12,588mAh
  • Efficiency of boost electronics – 85%

RavPower RP-PB19 15,000mAh Power Bank

  • Supplied input charge – 11,741mAh

Julian’s Postbag: #42 – USB 3.0 Power Monitors (Red/Yellow)

Two fascinating USB 3.0 power monitors which have super accurate voltage, current and power measurement and some really neat additional features.

USB 3.0 Power Monitor – YZXstudio Voltage Current Meter OLED Charger Doctor #YZXstudio

USB 3.0 Power Monitor (Red) YZXstudio Voltage Current Meter High Resolution OLED

Disclosure: These items were supplied to me at no cost for the purpose of making a review video.