Audible continuity tester...

[Externet]

Hi fellows.
At my previous workplace, we used an extremely simple gadget to verify continuity; I saw it once on the web, cannot find it now.

If anyone knows it please help , it is a generic black box about the size of a pack of cigarettes, aluminium cover, made in USA somewhere around LosAngeles as I may remember, model something like BP-1; has a 2" speaker inside, a T0-92 something, a mini transformer, a resistor and a 9V battery.. Nothing else !
Produces a tone from 200 Hz at 0 Ohms to 2KHz at 200 Ohms, also tests leds in-circuit by turning them on.

Does anyone has one?
Miguel

[Chris Smith]

A simple 555 and a speaker.

When the two leads come together the speaker oscillates, on.

Several ways to use it, in a large bunch of wires simply tie two wires together and then at the other end use the sound generator to see if they both have continuity. Up one, down the other.

Or with a single wire you can ground it and ground one of your leads using the other as a continuity check.

Even attaching one wire to EARTH ground, a good ohm meter will do the same at high settings.

[Robert Reed]

Is it just an audible continuity tone that you are after or do you actually want to discern the difference in that range of "near" continuity impedances?

[haklesup]

I got two of those (one broken).

2.5"x3.65"x1.5"
Bakolite box (yeah, not ABS, its that old)
with aluminum cover having holes for a speeker and markings:

Mini-Beeper
Model MB-1
EREM
Torrance California

Inside is 1 C size battery in a clip, one 8 ohm speaker, and one small PCB containing a small audio transformer (TL001) (presumably impedance matching type, 4 pins), A transistor (KB6041, T 103) and a resistor (faded but looks like green, blue, red, gold and meadures 710ohms in circuit). Thats it. No date codes on anything

Sorry, I would need to break the glue holding the PCB to get a circuit but you can probably puzzle it out from here.

You could make a similar out of a 555 (or almost any oscillator circuit) but this box I have predates the common availability of even that old part#. To do it with a 555. Design an oscillator that outputs an audio frequency. the design should include a resistor. Open that node and place the probes within. A short makes the tone you described and higher resistance causes the oscillator to decrese its frequency causing a lower tone until it drops out as it approaches an open.

Unfortunately, these are essentially obsolete since just about every DMM made has a beep continuity mode that applies less current in most situations. Having the variable audible tone makes it easier to tone out resistive connections in connectors and cables and low impedance loads like diodes (FB) and small resistors, you can hear the difference either side of a bad connection or small load. Intermittants sound more crackly than with a DMM too.

[Externet]

Bingoooooo !

Thanks, haklesup !
That has to be the one. But even with the brand information you now provided, does not show up on the net.

I prefer not to make a 555 one, am curious of the extreme simplicity of that one.

If you sell the broken one let me know. Am local in Brisbane and visit Santa Clara often. Would be a pleasure to shake your hand.

Miguel

[Chris Smith]

You wont find more sensitive, simplistic wiring, or any thing else than the 555.

The circuit for the 555 cost over $200 back in the early 70s simply because of it parts count, accuracy, and simplistics.

Today it will give you everything you need for a dime, [or less] while the speaker should set you back at least 50 cents.

[Externet]

Thanks Chris, I have 200 pounds of parts to build circuits to do it but I do not want that on a 555

[Chris Smith]

Exter...Sounds like you have had bad experiences with the 555?

I have used Forest Mimms books since the early 80s, [better than the manufactures books],... I have learned more from the 555 than most circuits, and never have I had a single failure.

[Except my mistakes of pushing it way too far]

Instead My intuition has pushed the boundaries that he has set way past the norm by factors of 10 to 100.

One touch sensitive circuits would go off "near" the device feet away instead of the actual touch , and another photo transmitter was supposed to do inches yet did more than ten yards, while a sound sensor could hear a cricket pass gas at 100 yards when it was supposed to go off from a local hand clap.

My sound generator for "opens and shorts" was the best usable device I had made in the 80s, for house, automotive, and just about every thing else.

And it cost me two bucks.

I still have it.

[dacflyer]

i have here a small box, its called the little bitty tester.. it is a transistor tester,,,and continuity etc,
has a polarity sw. for pnp npn transistors..with bi-color led and a buzzer.
perhaps this might work for you ??
if you need more info, i will post it this evening

[Robert Reed]

If its just a GO-NO GO tester for continuity, try the one I used in wiring up my house. One SONALERT with a 9 V battery. I didn't even put it in a box, just taped the battery to the SONALERT with a couple of two foot test leads. I used this for IDing homeruns back to the box. This was 10 years ago. The other day I fished it out of a dusty crate in the garage and inspite of all that time in storage, it still worked (original battery).

[Externet]

Thanks, Robert.
The gadget I mentioned is of variable audio, with a brutal simplicity guts; that is what has me interested, learning its operation principle.

Haklesup :
Found an ex-coworker and he remembered the brand. Now I found it on the net, same style, different label : Excelta

http://www.excelta.com/marketplace/brow ... tegory=339

Thanks all
Miguel

[haklesup]

The problem with the 555 design is that it needs to be seperately powered from the sense loop. You would need to turn it on to use it and then turn it off later to save the battery.

In the MB1 the power and sense current is supplied through the test leads. When not sensing continuity, the circuit is entirely unpowered. The battery in mine has got to be 5-6 years old and it still works (we rarely use it, I had to search for it, still haven't found the other I thought we have)

The photo of the BP1 is so incredibly similar to the MB1 right down to the style of probe tip and the strain relief lacking opening for the test leads. Only the silkscreen is different. I bet they made so many way back then, they are still selling the same stock.

Now, can you find someone who actually stocks it?

Ill post a photo and schematic later

[Edd]

.

Initially ....what happened to the foe-rumm for a spell...did Al and Bodgy simultaneously try to delete a Spammer and the WHOLE BB system defaulted ?
Or was Michael K.. trying some involved system "mortifications" and then finally realized that he was definitely in some really deeeeeeeeeeeep do-do ?

One more circuit posibility to consider:

Digging into my circuit archives collection, here is one circuit with the option of sensing levels (semi junctions..or not), using two probe options.
It is using a triple darlington set of discretes supplying power to a FF osc ckt that generates the spkr audio.
It uses only a few discretes (200 lbs) and its PCB layout is included at the bottom link.




From.....http://www.uoguelph.ca/~antoon/circ/cntnuity.htm

73's de Edd
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Five out of four people have trouble with fractions.

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[Dean Huster]

I wish all these DMMs with the continuity function HAD variable frequency so you could tell the difference between a dead short and several tens of ohms of resistance. It's amazing how many folks think that just because they hear the continuity tone from their high-end Fluke handheld, they think they have a perfect connection.

Dean

[Robert Reed]

I only use my Fluke continuity tone for quick cable identification and its a blessing for that. I would not even consider it for criticlal lo-ohms measurements.