Digital Telemetry with ATMega8

The ATmega8 microcontroller-based Low-Cost Telemetry Device (LTD) is an efficient telemetry keyer. The LTD measures the voltage levels of up to four analog channels via its on-chip 10-bit ADC, converts the measurements to numbers, and then sends the data in Morse code to an external transmitter and to an attached RS-232 terminal. It can be set up either by the RS-232 terminal, in which case, a character string, such as transmitter ID, can can be sent, or it can be set up with only jumpers to ground. Parts count is very low, in part because the ATMega8's internal clock is used for timing.
Digital Telemetry with ATMega8 - schematic

The Low Cost Telemetry Device (LTD) provides a low cost, minimal parts count Telemetry keyer using an Atmel's ATMega8 Microcontroller. The LTD sends data by measuring voltage levels of up to four analog channels via its on-chip 10-bit Analog to Digital Converter (ADC) and converting them to numbers and sending the measurements via Morse Code. There are two signal outputs - one is a binary Morse Code signal such as would be used to key a Continuous wave (CW) transmitter, and the other output is tone modulated and could be used to drive a small speaker to the audio input of a transmitter. Options allow setting code speed to 25, 10, 5 or 1 word per minute, 1 kHz or 500 Hz tone, and measuring 1, 2, 3, or 4 analog channels. The options maybe set with jumpers or with and EIA-232 terminal, and in the case of setting it up with a terminal, a text string of up to 80 characters maybe sent along with the data. Terminal settings are 9600 Baud, no parity. Thoroughly Modern Morse Morse code , now over 150 years old, has long since faded from use by Coast Guard, Navy and other Military Services in favor of modern communications modes usually carried over microwave or Satellite links. So one must ask , why use Morse code when we have things like Bluetooth or 802.11 to send data? The answer is simplicity and reliability. When Samuel Morse demonstrated the Telegraph to Congress in 1844 it was clear that one of the key features of...

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