Uses mathematical one-way functions. The private key must be kept private. The public key can be openly distributed without compromising security. Any person can encrypt a message using the public key. The encrypted message can only be decrypted with the private key. Using public-key cryptography to enable symmetric-key cryptography A typical example of how public-key […]
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Modbus Comms RTU
RTU is the binary version of Modbus (not ASCII) Modbus RTU over serial Byte Function0 Address1 Function code2:# Data# CRC Modbus RTU over serial – Function 3 See here Modbus RTU over serial – Function 6 See here
Antenna separation
A basic rule: The horizontal distance between antennas should be greater than 1/4 of its wavelength (absolute minimum separation), but it should not be located at the exact multiples of its wavelength (maybe avoid the first 3-4 multiples). If multiple frequency antennas are near each other, then use the spacing distance of the lower frequency […]
Terminating resistor
A RS485 bus needs a 120ohm resistor placed at each end of the cable run. Software switched terminating resistor This circuit works well for digitally switching in a terminating resistor:
DMX Values
16 bit values 16 bit values are usually sent MSB first, or as course/fine where course = channel, fine = channel+1
SPI Mode
Mode CPOL CPHA 0 0 0 Clock idle low, data is clocked in on rising edge, output data (change) on falling edge 1 0 1 Clock idle low, data is clocked in on falling edge, output data (change) on rising edge 2 1 0 Clock idle high, data is clocked in on falling edge, output […]
MOV (Metal Oxide Varistor)
A MOV is normally open circuit. If the voltage across it exceeds its nominal rated voltage it will very quickly clamp it by becoming very low impedance, shunting an overload through it for instance. When shunting a MOV is dissipating all of the energy across itself and therefore it’s often used in combination with a […]
PTC / Thermistors
PTC stands for Positive Temperature Coefficient and is simply another name for a thermistor. A PTC device will have a nominal resistance, for instance 1kohm, that it is normally at. If it gets hot then its resistance increases. PTC’s are often used to protect inputs for instance in multimeters but not they are no fast-acting. […]
Resistors voltage tolerance
Increasing voltage capability Place resistors in series. For example, 5x 200kohm 100V resistors is equivalent to 1 x 1Mohm 500V resistor. Using multiple lower voltage resistors is often cheaper than a single high voltage resistor. Also multiple resistors provides increased creepage distance against a single resistor of the same footprint (can be handy to avoid […]
Multimeter Input Stage
Input Impedance Voltage Measurement Most multimeters will have an input impedance of 10Mohm. This means it will effectively apply a resistance across what you measure of 10Mohm, potentially affecting the measurement if the source has a high impedance Current Measurement Will depend on the meter, but it might be say 1ohm for the mA range […]