Digital potentiometer

 
Digital potentiometer

What is a digital potentiometer? A digital potentiometer (also known as digital resistor) has the same function as a normal potentiometer but instead of mechanical action it uses digital signals and switches. This is done by making use of a ‘resistor ladder’, a string of small resistors in series. At every step of the ladder, an electronic switch is present. Only one switch is closed at the same time and in this way the closed switch determines the ‘wiper’ position and the resistance ratio. The amount of steps in the ladder determines the resolution of the digital pot. The diagram below shows the working principle of a digital potentiometer with 64 steps. Digital resistors can be controlled by using simple up/down signals or by serial protocols such as I²C or SPI. Digital potentiometer definition A digital potentiometer is a variable resistor which is controlled by digital signals instead of by mechanical movement. Properties of digital potentiometers Digital potentiometers are integrated circuit (ICs), some variants have a nonvolatile memory (EEPROM) which remembers the ‘wiper’ position. When there is no on-board memory, the initial position of the wiper is often the middle position. Because of their relatively small size compared to conventional potentiometers, multiple potentiometers can be packed on a chip and ICs with up to 6 channels are available. The amount of steps available determines the resolution of the digital potentiometer. The following table lists common step values available, including the bit count: Number of steps Bits 5 6 7 8 9 10 Steps 32 64 128 256 512 1024 Digital resistors are available in a range of values, but 10 kΩ is the most used. Other common values are 5, 50 and 100 kΩ. The standard tolerance is 20% but nowadays digital potentiometers with a tolerance down to 1% are [… read more]

Variable resistor

 
Variable resistor

What is a variable resistor? A variable resistor is a resistor of which the electric resistance value can be adjusted. A variable resistor is in essence an electro-mechanical transducer and normally works by sliding a contact (wiper) over a resistive element. When a variable resistor is used as a potential divider by using 3 terminals it is called a potentiometer. When only two terminals are used, it functions as a variable resistance and is called a rheostat. Electronically controlled variable resistors exist, which can be controlled electronically instead of by mechanical action. These resistors are called digital potentiometers. Variable resistor definition A resistor of which the ohmic resistance value can be adjusted. Either mechanically (potentiometer, rheostat) or electronically (digital potentiometer). Types of variable resistors Potentiometer The potentiometer is the most common variable resistor. It functions as a potential divider and is used to generate a voltage signal depending on the position of the potentiometer. This signal can be used for a very wide variety of applications including: Amplifier gain control(audio volume), measurement of distance or angles, tuning of circuits and much more. When variable resistors are used to tune or calibrate a circuit or application, trimmer potentiometers or trimpots are used, this are mostly small potentiometers mounted on the circuit board, which can be adjusted using a screwdriver. Rheostat Rheostats are very similar in construction to potentiometers, but are not used as a potential divider, but as a variable resistance. They use only 2 terminals instead of the 3 terminals potentiometers use. One connection is made at one end of the resistive element, the other at the wiper of the variable resistor. In the past rheostats were  used as power control devices in series with the load, such as a light bulb. Nowadays rheostats are not used as power control anymore [… read more]