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USB Voltage Levels
High and Low Levels Transmit On low and full speed devices A differential ‘1’ is transmitted by pulling D+ over 2.8V with a 15K ohm resistor pulled to ground and D- under 0.3V with a 1.5K ohm resistor pulled to 3.6V. A differential ‘0’ on the other hand is a D- greater than 2.8V and […]
Measuring High Voltages
EEVBlog video 932 has a great teardown video about this here.
Zener Diodes
Zener diodes allow current to pass in the normal direction just like any normal diode and with the 0.6V ish drop, again just like any normal diode. Whats different about them is that, unlike a normal diode which blocks current in the reverse direction (until you hit its reverse breakdown voltage), a zener diode will block […]
Troubleshooting CAN Bus
A few tips on trying to get a CAN bus to work… Baud Rate Check the baud rate is good using an oscilloscope. If the baud is 250k for instance, that's 1 second / 250000 = 4uS per bit. You should be able to see 4uS individual bits being sent (the SOF at the start of a […]
Parallelling Mosfets
The characteristics of paralleled mosfets will not be guaranteed to be exactly the same due to manufacturing differences, tolerances etc, so your design needs to allow for this. Heatsinking Paralleled mosfets should be placed close together and use the same heatsink so they are thermally matched. Current Sharing Resistor You typically need to use a source […]
Over votlage driving CMOS pins
CMOS inputs on virtually all CMOS devices, from the humble 74HC00 to super complex microcontrollers, incorporate protection diodes internally to GND and to VCC. Not all data sheets show them, but they are there to protect the device from being damaged by any over voltage on the input however brief. Is it OK to actually use these diodes – yep. […]
Higher Voltage Interfacing
Higher Voltage Inputs A 74HC4049 or 74HC4050 can be powered at 2V to 6V and will accept input voltages up to +16V (pin out is same, 74HC4049 just inverts the logic state). 4049 is basically the same but consumes a bit more current and has a min supply voltage of 3.5V. Higher Voltage Outputs Low […]
Cable Quality
Are expensive HDMI cables worth it? Yes and no. Below around 2m length no it is unlikely to make any difference. At longer lengths yes, but not because fancy pansy "high quality" cables are better and will make the picture or sound better, but because the cable needs to be compliant with the HDMI specifications and have been tested to […]
Max Cable Length
HDMI Cables The video and audio data channels of an HDMI cable are capable of traveling over long distances. The DDC (Display Data Channel I2C bis) limits the cable length of HDMI cables. According to an expert who tests cables for compliance, going above 18m even with the best cables requires active repeating of the DDC connection.