After receiving the DTMF signal, MT8870 internally divides the signal into high and low frequency bands, and sends this signal to a digital decoder. The key values are decoded by the digital decoder, and then the decoded key values are output in binary form on four lines (Q1, Q2, Q3, Q4) to an external shared bus. It is worth mentioning that when MT8870 solves a key value and outputs it to the outside, its STD pin will rise from low state to high state, and then fall back to low state after a period of time. We can use this feature to detect the signal on this pin and immediately read the value generated by Q1-Q4 pins into the CPU, and then solve the key value of the phone.
PRODUCT INFORMATION:
Supply voltage: DC 5V
Peak current: 10mA
Working temperature: -65 ℃~150 ℃
Peak power consumption: 500mA
