If a custom hardware design is being used, there are some additional components which need to be considered. Depending on the characteristics of the ultrasonic transducer being used, there may be a need for additional circuitry between the AVR device and the transmit and receive lines of the sensor. For instance, the pins on the AVR may not have sufficient drive capability to initiate an ultrasonic transmission, meaning that a push-pull amplifier would be needed between the output pin of the AVR and the TX line of the transducer. Additionally, the transducer RX line signal will need some level of amplification and filtering before it can be effectively received by the AVR analog comparator. The design of these elements will depend on the application. For reference, see the Ultrasonic Distance Measurement Field Engagement Board schematic.