Bosch Balderdosh?

[Huge]

Haven't we all, haven't we all.

[Andy Burns]

Yeah well, you need to keep it for whenever you need to replace the element on your Antex, eh?

[Johny B Good]

Tactile feedback can't inform you of a dead battery.

That suggests a 12v battery rather than a lithium coin cell or two. Putting the led in series is a rather neat way of maximising battery life when you've got 12 volts worth to play with.

It's neat in the sense that it not only indicates a good battery but can also can indicate a circuit fault elsewhere as well as avoiding the need for a seperate dropper resistor to limit the LED current to something similar to what the whole TX circuit takes. In effect, the TX cct substitutes for the current limiting resistor, reducing the component count which contributes to an improved reliability.

I can't see the TX cct needing any more than 10mA which is well within the rating of even the smallest of smd chip LEDs. It was just 'bad luck' that the LED failed in this instance. I don't think that would be a very common failure, they're usually good for in excess of

100KH at 'indicator' current draw levels.

A rhetorical question I think (we're all too familiar with the auto industry's practice of applying "Russ Andrews Pricing" on items like this).

And, a jeweler's loupe to go with those needle tips? :-)

[gareth]

The failure of movement of the garage door will tell you that.

9v PP3. The LED will not current limit to save battery life.

Except in this case, the redundant LED contributed to reduced reliability.

What happens when you combine a joke with a rhetorical question?

I've 3 loupes of varying dioptres.

[Johny B Good]

That only tells you that something in the overall system failed. A flat GDO battery is merely one possible cause. If the GDO kit had included a spare GDO fob, you could have determined whether it was a keyfob fault or in the RX controller of the GDO mechanism attached to the door. The GDO fob is not the only point of failure.

I didn't say it would (it's in series). The diode provides a pretty stable volt drop, circa 1.7v iirc, over a wide range of current levels. Since the TX cct can work reliably with a voltage range of 5 to 7v (as it must in this cct arrangement), substuting the TX cct for a seperate 470 to 680 ohm dropper resistor that would be required to give the LED sufficient brightness more or less halves the total current consumption of the GDO.

Considering the very tiny risk of the LED going open cct, I'd say it was a wise choice on the part of the designer.

No arguing with that statement but statistically, no worse than a component failure elsewhere in the TX cct. It's true that incorporating 3 slicon diodes across the LED could have guarded against this particular failure but the ROI value of the extra components wouldn't be sufficient to justify the extra production cost.

Such are the conflicting design requirements of mass produced electronics in the real world. Welcome to the real world. I'm afraid to say, this is a mild example of 'penny pinching', there are far worse examples you can rant about with plenty of other similar gadgets (and much more sophisticated electronic gear as well).

I don't know! (this had better be good). "What does happen when you combine a joke with a rhetorical question?"

Right answer! :-)

[gareth]

Sorry, it was a rhetorical question.