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Postbag Index – the Seventies

Julian’s Postbag: #73 – eBay Electronics Haul

  • WS2812 DC5V/WS2811 DC12V Mini Controller 76 Effect Control 2048 Pixels Bulit-in
  • USB Charger Doctor Current Voltage Charging Detector Battery Voltmeter Ammeter
  • 2PCS RGB LED Ring 16Bit WS2812 5050 RGB LED + Integrated Drivers For Arduino
  • 7-Bit 8-bit 12-bit 16-bit 24-bit 60-bit WS2812 5050 RGB Lamp Panel Round LED
  • 1PCS NEW 5V PIC12F675 Development Board Learning Board Breadboard L87
  • 10pcs Micro USB Charger Module 5V 1A 18650 Lithium Battery Charging Board TP4056

Julian’s Postbag: #72 – Beautiful Multi-Colour Flashing LEDs

  • DC 5V 50PCS WS2811 RGB Full Color 12mm Pixels digital Addressable LED String
  • 21Key LED Symphony IR Remote Controller For WS2811 WS2812B LED Strip Light DC 5V
  • DC5V 12V 24Key IR Remote Controller WS2811 WS2812B Pixel LED Strip Light Module
  • 8A Li-ion Lithium Charger Battery Protection Board LED Capacity Indicator 18650
  • 100A 60V DC RC Helicopter Airplane Battery Power Analyzer Watt Meter Balancer
  • Premium Mens Womens LED Digital Sports Silicone Bracelet Waterproof Wrist Watch

Julian’s Postbag: #71 – More Fun Electronics Stuff from China

  • B0505S-1W DC-DC 5V Power Supply Module 4 Pin Isolated converter NEW
  • Digital LCD TDS EC TEMP PPM Meter Tester Filter Pen Stick Water Quality Purity
  • 2pcs 0.9V-5V to 5V DC-DC Booster Module USB Mobile Step-up Power Supply Module
  • INA219 I2C Bi-directional DC Current Power Supply Sensor Breakout Module
  • Digital LCD Indoor Temperature Humidity Meter Thermometer Hygrometer
  • Digital Cigar Humidor Hygrometer Thermometer Round Black Face
  • Flexible Stranded of UL-1007 24 AWG wire cable Yellow/Blue/Red/Black 10M 300V
  • microcontrollers PICkit2 PIC KIT2 debugger programmer for PIC24 PIC32 PIC dsPIC
  • PICkit3 PIC KIT3 Debugger Programmer Emulator PIC Controller Development board

Julian’s Postbag: #70 – Ten Items in Ten Minutes (well almost)

  • Qi Wireless Fast Charger Charging Pad for Samsung Galaxy S6/S6 Edge Note5 Nexus4
  • Digital LED Constant Current & Volt Regulated Power Supply Step-down Module
  • DC High voltage Generator Inverter Electric Ignitor DIY Kit for 18650 Battery
  • Fashion Child Kid Silicone Date Multi-Purpose Electronic Wrist Calculator Watch
  • Flashing LED Glow Light Up YOYO Party Colorful Yo-Yo Toys For Kids Boy Toys Gift
  • Durable Analog Hygrometer Humidity Meter Power-Free Indoor Outdoor High Quality
  • Dual USB 5V 2A 6x 18650 Power Bank Battery Case Box Charger Box For Cell Phones
  • KWS-V20 USB LCD Digital Current Voltage Doctor Capacity Tester Meter Voltmeter
  • New 1M Micro USB Data Charging Voltage Current Cable Cord For Android Phone
  • Ultra Thin Wireless Power Charging Pad Receiver Tag for QI Android


Julian’s Postbag: #69 – More Electronics Stuff from eBay

  • 100pcs 10 x 1 mm Neodymium Disc Super Strong Rare Earth N35 Small Fridge Magnets
  • 1PC Farad Capacitor 2.7V 500F 35*60MM Super Capacitor 2.7V500F
  • AD584 High Precision Voltage Reference Module 4-Channel 2.5V/7.5V/5V/10V
  • DC 5V-32V to 1V-30V 10A LTC3780 Automatic Step Up Down Regulator Charging Module
  • Bluetooth Smart Wrist Watch Phone Mate For IOS Android iPhone Samsung HTC LG

Julian’s Postbag: #68 – Why do I buy all this eBay stuff?

  • Smart Voltage Current LED Display Micro USB Sync Data Fast Charging Cable 1.2M
  • Geneva Women’s Candy Color Quartz Watch Round Dial Analog Indicate Rubber Band
  • New Anti Gravity Revolution Magnetic Levitation Device Science Educate Toy
  • Check out 10PCS Card Lamp Bulb Led Keychain Mini LED Night Light Portable USB Power White
  • Black 7-Port USB 2.0 Hub with High Speed Adapter ON/OFF Switch for Laptop PC
  • Farad Capacitor 2.7V 120F 6pcs Super Capacitor With Protection Board Module

Julian’s Postbag: #59 – Wonderful Tech or Worthless Tat?

  • DC-DC Converter Isolated Power In 10V-16V Double Out 5V
  • Multifunction 60W Constant Current Electronic Load Battery Capacity Tester Module from Banggood
  • OLED Smart Wrist Band Bracelet Watch Pedometer Bluetooth for Android IOS Orange
  • Creative DIY 4 IN 1 Educational Learning Power Dragon Solar Robot Kit Kids Toy $9.99

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.