A 2.4GHz High-Power Audio-Video Link

Forget about flea power A-V links. This one has an output of 0.5W for a range of about 200 meters using simple "whip" antennas.


You will have seen adverts for devices of this type - they've become quite popular in recent years.

Operating on a frequency of 2.4GHz (that's 2,400,000,000Hz for the uninitiated!), most have about 10mW or so output and while they work well over a short range, the range is limited by the low power.

This design has much higher power - around 0.5W output, in fact. So as you might expect, the range is very significantly extended. With the simple coax cable "whip" antennas shown here, the range is reliably 200m or more. But if you use a simple dipole antenna, you could expect much more range - maybe 10 times or more.

Perhaps a word or two about how and why this is possible is in order. It is sometimes difficult for people to understand how changing antennas can give longer range.

The simplest analogy I can think of is using your own voice. You can talk at a certain level and you'll be heard up to a certain range. You can shout, and of course you'll be heard by people further away. You're increasing the power of your voice.

Or you could cup your hands around your mouth and project your voice in a certain direction. Those off to the side won't hear as much (if at all) but those in the direction you're projecting will hear much more.

That's the equivalent of using a directional antenna. You're concentrating power in one particular direction at the expense of other (unwanted) directions.

If you replaced your hands with a long length of pipe, those to the side would hear little, if anything. But those at the other end of the pipe, even over a very much longer distance, could possibly hear you.

That's the equivalent of using a highly directional antenna. Very little energy is radiated in any direction except the one you want.

OK, now that we know how to get longer range by increasing power and/or using directional antennas, let's get back to the Audio/Video Link.

NOTE: ALL OF DATA OR METERIAL ON THIS BLOG IS JUST ONLY FOR STUDYING OR LEARNING PURPOSE ONLY,

45-Second Voice Recorder Module

45 second message recording without tapes or discs. Use it for phone messages, a voice memo pad, you name it!

When you need to record voice messages with the highest possible reliability, there’s no substitute for a solid-state voice recorder chip. There are no moving parts at all, so there are no tapes or belts to break, no heads to clog up with gunk, no motors to burn out and no bearings to jam. Instead, there’s just a memory chip to store and replay the message electronically, any number of times.

Because it’s solid-state, the message(s) can be played back instantly – there’s no tape to rewind. Small wonder that most telephone answering machines changed over to this kind of recording years ago.

We’ve described solid-state voice recorder projects in the past and they’ve been very popular. However, the special chips they used eventually became hard to get and so these projects eventually fell by the wayside.

This situation recently changed for the better again, when Jaycar Electronics managed to find a good source for a new voice recorder IC, the HK828. This made it possible for us to develop a new recorder design, incorporating not only the features that were popular in the earlier designs but a few more based on the requests we’ve received from readers over the years.

The new HK828 chip can store single or multiple messages with a total length of between 40 and 60 seconds, depending on the sampling rate and the voice quality you want. In our new recorder module, this chip is teamed up with a low-cost electret microphone to allow easy message recording, plus an LM386 power amplifier IC which allows the recorded messages to be played back through a small speaker.

In addition, we’ve made provision for the module to be hooked up to a 600Ω/600Ω line isolation transformer for coupling into another system; eg, an alarm system or a private phone line. There’s also a simple interface so that the module’s functions can be controlled via a PC or microcontroller.

The new recorder module runs from 6V DC and draws very little current, so it’s quite suitable for operating from either a battery (eg, four AA penlight cells) or from a regulated 6V plugpack supply.

By the way, since the HK828 voice recorder chip is only available from Jaycar Electronics in Australia and New Zealand, kits for the new recorder will only be available from Jaycar and its dealers

NOTE: ALL OF DATA OR METERIAL ON THIS BLOG IS JUST ONLY FOR STUDYING OR LEARNING PURPOSE ONLY,