Design 65~240Hz single tone circuit based on SN7490

1206RGB (single)

Single chip microcomputer STM32L151CCU6

0201 package SLP0603 ESD electrostatic diode 5V one-way ESD

Car Audio Crystal 3.2*2.5mm 3225 24M (24.000MHZ) 20PF 10PPM 20PPM 30PPM

inductance

The output of the counter SN7490 is a two-decimal number. The output of the data selector is fed back to the reset input of the SN7490, that is, a pulse is output at the end of each counting cycle, and the pulse simultaneously resets the counter SN7490. The output pulse width is 60ns, which is determined by the transmission delay time of the circuit. With this non-frequency cascading, a frequency divider with a larger division factor can be constructed.
The output of the 65~240Hz crystal oscillator is divided by 1000 times in three SN7490s, and a single tone of 65~240Hz is obtained, which is fed to the amateur FM player. The crystal is chosen to give the exact design frequency. Q1 and Q2 are MPS6513 and Q3 is 2N1613. The battery source can be a 9~15V DC or 9V battery from the transceiver.