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Half-Duplex With HopeRF's HM-TR UHF Transceivers

Our introductory second-generation UHF data transceiver article in October 2008 showed that using a PICAXE to drive HopeRF's HM-TR 433MHz programmable data transceivers works well. In subsequent months, these well-priced units have become very popular!

By Stan Swan

For those who have just come in, these Chinese-made UHF FSK data transceivers, selling locally for ~$25 (via MicroZed, the Australian PICAXE distributors) offer tempting programmable features in a 6-pin SIP “one-stop” package. They have been found well-suited to more professional 433MHz ISM applications.

Click for larger image
Fig.1: This simple PICAXE-08M circuit gives half duplex control of the HM-TR 433MHz data transceiver and has very low hibernation current.

Thanks to a quality-fitted antenna socket, even the supplied “rubber ducky” antenna allows line-of-sight (LOS) ranges of up to 1km, with performance in demanding conditions superior to cheap classic individual 433.92MHz transmitter/receiver offerings – many of which unfortunately have insensitive receivers.

Conditions in crowded Asian cities apparently favour the 433MHz UHF band for the likes of slow wireless utility data from water and electrical meters. Microwave level 2.4GHz data links do not have the necessary punch-through for numerous obstacles and so quickly suffer attenuation.

We focused on the more versatile RS232 versions in the initial SILICON CHIP article but this month the “barebones” TTL transceiver types will be considered. These TTL versions offer very low (µA level) supply current “sleep” benefits and may also be slightly cheaper, as a MAX232 IC is not fitted to them.

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