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Picaxe-08M 433MHz Data Transceiver

Telemetry (from the Greek tele = remote and metron = measure) refers to the remote measurement and reporting of information, typically using wireless links to carry the data. Such technology is well established in climatic monitoring (especially temperature), water management, motor sport, security, medicine, defence and even space - Martian probe style.

By Stan Swan

Wireless telemetry (using high voltage valves) was utilised even back in grandpa’s era.Perhaps one of the more exotic installations was the World War II German automatic weather station "Kurt", secretly installed on the Canadian coast by a U-boat in 1943.

Its 150W short-wave transmitter, powered by an array of nickel-cadmium and dry-cell batteries, produced coded signals (derived from weather sensors) receivable thousands of kilometres away in Europe. Distant Atlantic weather conditions could then be monitored but – fortunately for Allied shipping – jamming thwarted the station’s eventual mission!

Click for larger image
The HopeRF module that has Stan so excited this month! Shown here approximately life size, it operates in the 434MHz "LIPD" band and mates perfectly with Stan's other favourite toy, the PICAXE.

Modern motor racing telemetry allows trackside engineers to view and interpret live race data and use it to rapidly tune their racecar at eventual pit stops. When every second counts, the ability to promptly work on tele-monitored faults can make for improved race performance.

Such "mission critical" applications usually have heavy duty telemetry budgets but the availability of cheap data modules in recent years has allowed UHF wireless data links to proliferate, with many homes even now having several quietly at work – typically at 433.920MHz.

As wireless links on the higher (near microwave) 1.8-2.4GHz bands are almost line of sight (LOS), many field telemetry setups in fact prefer low UHF (300-900MHz) or even lower VHF (30-300MHz), as this ensures better signal penetration of vegetation and buildings.

The popular 434MHz slot, globally reserved for low power (25 mW) unlicensed Industrial, Scientific and Medical (ISM) wireless data, increasingly abounds with weird signals arising from home weather stations, power meters, car locks, garage door openers, security systems and wireless doorbells. In many suburbs at peak times, a UHF scanner tuned to 434MHz can issue sounds akin to an African dawn chorus!

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