Monitor circuit for 7-segment LED display - includes matrix assembly with resistor connections to transistors and error connection provided through window discriminator

摘要

The monitor unit is for a multiple setting time multiplex controlled numeric display unit, esp. the type provided with a 7-segment LED display unit. Each segment display control circuit comprises a pair of transistors (Tr12, Tr22) connected between the low voltage (e.g.5V) power line and earth, with collector terminals on the same side and separated by an LED (21) and a biassing resistor (R36). In parallel with the latter and also connected to the low voltage supply is another resistor (R26) forming part of a matrix assembly. The mid-point between the LED and the biassing resistor are coupled to a window discriminator (82) provided by a commercially available integrated circuit element. The output of the discriminator provides an error connection signal to a logic circuit including NOR gates and NAND gates.