Transmissive Backlight is required. Displays not easily read in sunlight Transflective The reflective properties allow the display to be read in bright sunlight where the backlight fails. Transflective displays are typically more expensive due to the manufacturing process. LCD Screen Viewing Angle Look at the LCD front on and imagine a 45º cone coming out […]
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RC Filter
RC calculation T=RC, so: Time Resistance Capacitance or mS Kohms uF or Seconds ohms F The result gives you 1T. This is 1 time period. So for 1000uF and a 1K resistor T = 1000mS For charging and discharging a capacitor: 1T 63% 2T 86.5% 3T 95% (this tends to be the default usage with […]
Ceramic Capacitors
Multilayer ceramincs are great for applications where voltage is constant (ie. you are smoothing off a voltage). However they are not good for use inline for AC voltages (i.e. audio and AC signal filters). The reason is that ceramic capacitors will give a piezo electric effect to an AC signal, which causes noise. For audio […]
Switchmode DC-DC Converter Design Notes
The following diagrams are taken from: http://www.analog.com/library/analogdialogue/archives/41-06/ground_bounce.html Buck DCDC Converters This is bad: This is good: Boost DCDC Converters Ground Bounce Design Tips Switcher IC’s with internal mosfets tend to aim towards higher efficiency and therefore lower mosfet on resistance. However low on resistance means faster switching times, which contributes to noise and ground bounce. […]
Thermistors General
Good Thermistor Calculators http://www.thermistor.com/calculators.php http://www.absorblearning.com/media/attachment.action?quick=pq&att=1843
USB Power and Battery Charging
The +5V output from a USB hub is permitted to range from 4.75V to 5.25V (5V +-5%). For USB2.0 this range is changed to be 4.4V to 5.25V and for USB3.0 the range starts from 4.0V. A USB device is permitted to draw up to 100mA (1 unit load) for USB2.0, and up to 150mA […]
Using MOSFETs As General Switches
Basic MOSFET Selection Rules / Checks The Drain to Source max voltage rating (max Vds) determines the maximum voltage you can switch. The Gate threshold voltage determines the voltage difference you need to apply to the gate to make the mosfet conduct. The Gate to Source max voltage (max Vgs) is a critical factor that must not be exceeded (even […]
125kHz RFID Reader Design
RFID Circuit & PCB Design Notes It’s usually very important that the voltage supply to an RFID reader is protected from ripple and interference. Where you have noisy electronics in the proximity: A simple RC filter of 10R and 1000uF will go a long way to preventing interference. Better still is using a separate power […]
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Making a Jabra 9350e DECT headset work properly
The Jabra at 9350E is a brilliant DECT headset. It works as both a wireless USB audio headset for a PC and a wireless telephone DECT headset. Jabra also do the 9330 models which provide just one of these functions. We find the audio quality really good and also use it with Dragon Naturally Speaking […]