Hi guys. I build a FM transmitter based on the ba1404 chip. The problem arises because this chip need a 38Khz crystal for produce a subcarrier signal for the stereo transmition, but that crystal is hard to find. To solve it i programed a PIC16f84 to generate the 38 Khz signal and, depending of what crystal use for the PIC, i could reproduce the 38Khz fecuency more or less exactly. (For example wuth a PIC runing on a 4MHZ crystal a can generate a 38,4 Khz signal). What accurate such signal have to do?
Hi, thanks for the response. Yesterday i had the oportunity of measure the circuit with an osciloscope. The method of injecting the signal externaly seems to work. But I had a problem, because when conect the circuit and transmit audio trough it, it seems to be that transmit in stereo, but the L channel is not transmitted (while the right yes). I make a test: I connected R to 0V and L to a sine wave and something appears at the pin 14. But if i make the opposite( connect L to 0V and L to a sine wave) nothing happens.
I have three questions:
1) The signal that must appears at pin 14 is simply the conmutation between the channel R and the channel L ? (O maybe that signal filtered , but basically the multiplexing between the two channels, is correct?)
2) If I apply 0V to pin 5 (the "clock in") the signal present in pin
14 must be one channel and if conects nearly VCC to pin 5 in pin 14 appears the other channel, thats rigth?? Since when I transmit in stereo (though the R channel is not transmitted and I transmit only the L) the audio is listening something noisy, but if connect the pin
5 to 0V is clean.
3)Is possible that I have burned only the multiplexer?
4)Another story: the input impedance is 540ohm typically (ba1404 datasheet). I surprised, i think that it must be much more higher; that is the input impedance in pin 1 and pin 18?
5)Finally: I understand I have a poor level of english, so I thanks to you that you alert me ("BTW Get yourself a spell checker"), and that read the posts. two quiestions: * spell checker is for ortography not? But I think I have a poor level of Grammar also, is corect? * Whats means "BTW" ?