vlf transmitter, part II

The product is an Instafence (also called Instant Fence or wireless fence). The manual for the thing is available on petsafe.net, look for the PIF-300 product (which also includes the collar). It transmits a short range signal at 18.7 kilohertz using large air coils as antennas. It is designed to contain a dog within a 90 foot radius and to issue mild shocks if/when the pet attempts to leave the area. It does not work with a buried wire loop, it uses the transmitter to define the dogs play area.

For anyone interested in purchasing one, they are horribly expensive (list price $280) and they have a special battery for the collar, which is only used by petsafe, available at 6 dollars each. The batteries don't last long. The range is only 90 feet, so it doesn't allow the pet to move very much.

It appears to be grossly over-engineered as well, an ASIC feeds one each amplifier separately and the amps appear to run at very low power. No doubt a much cheaper transmitter could be made, this one is also physically large as well!

For anyone interested in the petsafe IF100 vlf transmitter, you can look on

for the manufacturers info-

Or, check out pictures, schematic and field strength documentation at:

Here are some notes based on my personal observations (before I returned the device).

SW2 is hardwired, and is not adjustable as shown in the schematic. For some reason, this switch was called 'mode' back in 1998 when petsafe submitted the documentation to the FCC. The schematic shows it as a switch though. When looking at the schematic, the position of the switch in the schematic is shown correctly.

Switching S3 to ground selects low power transmit.

The pot, R33 is the power control.

The ASIC is marked as follows: Supertex

500-029 204T770 0225

It is impossible to tell how many turns are on each loop (transmit antenna). But, each of the 4 loops has the same size wire and has a dc resistance of 4.5 ohms. Vdd for the ASIC is 4.85 volts.

I have spectral output for each of the output lines (X, Y, Z). The spectral display shows the same signal on each output although the same output signal on all 3 output lines, although there are different peak amplitudes (some of the amp stages are driven harder than others, but all have the same basic input signals).

There are 3 audio amp chips, they are each the LM 1875T. They can run

20 watts output, but the output power is much lower than 20 watts for each stage. This is based on the V+ being very low (16.8v) and the observation that the 1.8A wall wart (at 14v ac) runs very cool. Also, although the heat sinks for each stage are very small, they are barely warm to the touch.

If anyone wants to see the spectral output of the ASIC that feeds the amps, send me an emmail to:

K Y 1 K at pivot dott nett.

Enjoy,

A

Far more things than you can imagine are designed like this. On short runs it isn't cost effective to come up with an efficient design. Same applies to a lot of software!

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N

Thanks N.

Well, the audio amp chips might be cheaper than some chips that are less powerful. I know this happens sometimes.

Also, the manufacturer attempts to get a somewhat circular (3D) power distribution so the orientation of the transmitter is non critical (and is a circle). So, three transmit stages might be necessary-I notice each stage has slightly different voltage gain, no doubt to try and achieve a circular coverage pattern. So, three stages might actually be necessary.

But, ASIC's are very expensive to develop and this one doesn't seem to be doing much. Maybe it's cheaper to have an ASIC than to build a larger circuit board with discrete components?

GL.

A

"When you only have a hammer, everything looks like a nail".

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N