Mosquito alarm equivalents?

[The Medway Handyman]

Is that a Japanese cat?

[Iain Churches]

Are you still using the ear-trumpet I sent you for your birthday?

[Arfa Daily]

Yeah, ok, maybe you would need a small piezo horn and a driver transistor to ramp up a genuine mossy repellant into a teen annoyer, but such are available from Maplin for less than a fiver. And where do you get your 555's from that they are not stable enough ? I have been using them for the last

40 years at least, and have never had the slightest problem with stability up to hundreds of kHz in all sorts of temperature-hostile environments. Even if stability was a problem, it would be simple (and cheap) enough to trade the 555 for a cheapo crystal with a CMOS divider on the end.

one in this spec sheet claims a temperature stability of 0.005% per degree C. The 'commercial' versions of the IC are specced for operation over the temperature range of 0 to +70 deg C. Whilst we may see outdoor temperatures somewhat below zero in the depths of winter, I think it is unlikely that the other end will be exceeded. Even if this did not prove stable enough, there are versions specced from -55 deg C to +125 deg C. The one in that link for instance.

We're hardly talking a precision application here anyway. Even if you did have to pay a tenner for the horn, you'd still have change out of 15 quid, even with a box to house it chucked in.

Arfa

[Arfa Daily]

Ouch ! :-)

Arfa

[Andy Dingley]

It's not the 555 itself, it's the crude charge pump circuit they're used in.

[Jules Richardson]

'Green' solution: Get a small cardboard box with a lid. Install a fine metal mesh under the lid. Fill the box with mosquitos. Open lid when undesirable youths are nearby.

Decorating the box and use of sticky-backed plastic are optional.

[Jules Richardson]

Interesting! That claimed my hearing was within normal range, which anyone who knows me well would tell you is bollocks ;-)

I found myself automatically making educated guesses at some of the numbers, though (similar to the way it's possible to read very blurry letters by shape clues I suppose) and maybe I wasn't supposed to be doing that - I don't think the test really said.

I suppose the background noise doesn't really change for that test, either - it's just hiss, and maybe that doesn't cause as much problem for me as some things (e.g. put me in a room with background conversations going on, or a radio playing in a car, and I have problems making out what someone's saying right next to me unless they talk quite loudly).

cheers

Jules

[Arfa Daily]

Yes, but it's not actually a charge pump circuit. It's a simple (not 'crude') R-C timing circuit, where the voltage across the timing cap is monitored by two comparators, which are used to control the discharge transistor across the cap. The cap is not 'pumped' over a series of cycles. It is merely charged and discharged to the same levels on each cycle.

If you use a halfway decent cap for the charging element, then the fact that it is a simple R-C network, is not an issue.

In any case, the 555 in all its forms, is plenty stable enough in itself, for a non-demanding application like this, but it wouldn't actually matter if the frequency wandered around +/- a kHz. Not that it would unless you went from having the circuit in a freezer, to waving a blowlamp at it ...

Arfa

[geoff]

But why does it matter - you just want a high pitched unpleasant noise no need for it not to wander a bit

555 timer? Stable enough for the requirement

[geoff]

In message , Iain Churches writes

My constant companion in the bathchair

[geoff]

Nah, just one which bites yer bum

[geoff]

Need a big box to house a couple of twin engined bombers, IWHT

[Huge]

That's deeply impressive. Not.

Server Error in '/' Application. The resource cannot be found. Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable. Please review the following URL and make sure that it is spelled correctly.

Requested URL: /howwehelp/hearing_check/take_online_hearing_check/_blank

Version Information: Microsoft .NET Framework Version:2.0.50727.3607; ASP.NET Version:2.0.50727.3614

[UnsteadyKen]

Thats just good old slrn breaking links. Get Pan and get with it.

[Huge]

Ummm. No. I went to the RNIB home page and followed their links to the test. It still broke.

I regard changing newsreaders (and text editors) with the same joy as abdominal surgery.

[UnsteadyKen]

I know what you mean, I used Forte Agent for donkeys and after 5 years using Gravity I think I'm on top of it. When I was playing with Ubuntu I tried slrn and Pan and favoured Pan more, just more comfortable with the interface.

[Jules Richardson]

Hmm, FWIW my copy of Pan (the newer release) still mishandled the URL and I had to remove a couple of stray characters before it'd work.

Here as a tinyurl if it's useful to anyone:

[Huge]

Server Error in '/' Application. The resource cannot be found. Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable. Please review the following URL and make sure that it is spelled correctly.

Requested URL: /howwehelp/hearing_check/take_online_hearing_check/_blank

Version Information: Microsoft .NET Framework Version:2.0.50727.3607; ASP.NET Version:2.0.50727.3614

It isn't looking for something on my (Linux) box, is it?

[dennis]

Its probably malicious but could be incompetence.

[Peter Larsen]

You convey the quite popular misunderstanding that hearing threshold is an expression of frequency response, it is not at all like that. The sense of hearing is auto-aligning itself to the properties of the transducer - the ear - as long as the sound in a critical band is above the threshold and has zero detection if a sound is below. A simple concept, except that the bands are bandpassfilters with a fairly low Q. That has the consequence that signal in a nearby band weighs in and helps tip the scale of detectability, something that explains that people with quite large threshold shifts may have completely valid impressions of the treble on a recording or at a live concert.

The auto-aligment feature is what makes it possible to "listen through" the frequency response variations of loudspeakers and rooms as long as a suitable "listen in" period is available. What is more important than mere frequency response is the amount of information, there is no information loss per se in a frequency response variation, but there is certainly a grave information loss in case of severe resonances or rattle and buzz, something that also the can be caused by mechanical malfunction in the middle ear.

Kind regards

Peter Larsen