555 multi-channel temperature test circuit diagram

The circuit is as shown in the figure, which is used to switch the thermocouples of the corresponding channels when testing multiple channels of temperature . Each channel uses 555 as the core to form a monostable delay circuit. If AN is pressed , pin 2 is at low level, IC 1 is set, pin 3 is at high level, J1 is closed, and the thermocouple of the channel is connected. Pass. At the same time, C1 charges it through R1. When the charging voltage reaches the threshold level of pin 6, 2/3Vdd, the 555 is reset and pin 3 turns to low level, which then triggers the second stage IC2, setting IC2 and turning on the third stage. Two thermocouples are triggered in sequence. If J1 is closed, cycle monitoring can be performed. The delay time (i.e. measurement time) of each stage is td=1.1R1C1, and the delay corresponding to the parameters shown in the figure is about 1 second. LED1~LEDn light-emitting diodes also light up in sequence as monitoring indicators.

When the circuit in Figure a is powered on, several LED light-emitting tubes flash at the same time. For this reason, the improved circuit is shown in Figure b. After connecting to the R and C network, when starting up, because the voltage on C cannot change suddenly, pin 4 of the reset terminal is in a forced reset state, and pin 3 is output at a low level. As the capacitor C is charged, pin 4 is in a high state. level, ICs at all levels are in a waiting trigger timing state, which improves the accuracy of the test.