Electronic Circuits and Tutorials
Electronics Schematics - M

Modem Circuits

BELL 103 Compatible FSK Modem Circuit - This circuit uses MM74HC942, a single chip low-speed modem which is compatible with Bell 103 standard. This Bell 103 modem circuit is run at 300 baud in full duplex (bidirectional). The frequency and sine wave synthesizer inside this modem chip generate phase-coherent FSK modulation for the best bit accuracy. Here is the schematic diagram of the modem circuit.

Power Line Modem Circuit for Home Automation Application - Imagine you have a master controller device that control other devices in your house, and you don’t need to install any additional wires to facilitate the data communication between the master controller and the controlled devices. Yes you’s life will be easier since all you need is just plugging your devices into your power line outlet, the devices will communicate each-other through the power line while using the line to enpower them! The secret is the powerline modem, a modem that use the powerline wiring as their media to exchange the data.

AM79101 / AM7910 Modem Schematic With RS-232 Interface for PC - This modem schematic started out in the pre-PC era and since has been updated with an RS-232 interface (MAX 203). I used what parts I had. A MAX 232 will do and is cheaper. A relay for the PTT circuit was used because of my Icom IC-730 that pulled a solid half amp through the PTT circuit. Modern radios are not built that way and so you might be able to use less parts in your design.

56K RF Modem:

900Mhz 9600bps Link:

Bell 202 and CCITT V23 Compatible FSK Modem Circuit - Using TCM3105 FSK modem chip from Texas Instruments, you can easily build a Bell 202 or CCITT V23 compatible modem. This modem circuit is capable transmitting the data at 75, 150, 600, and 1200 baud, and receive the data at 5, 75, 150, 600, and 1200 baud. This circuit operate at 5V supply and has low power consumption feature.

XR2206 and XR2211 - XR Chip Modem for RTTY and 'TOR Modes With RS-232 for the PC - The schematic is designed for RTTY and the 'TOR modes. It has somewhat of a RTTY squelch. The RTTY squelch action is handled by pin 6 being tied to pin 7. When there is no valid (locked) data pin 6 forces the data out line (pin 7) low.

Note: To report broken links or to submit your projects, tutorials please email to Webmaster