Electronics Q

Impressive. Bells as well?

Presumably with this level of attention to detail, you also try to operate the trains at scale speed. I once worked out that the average child operates their train set (as opposed to model railway) at a scale speed of over 300mph - and we are talking about a steam tank engine.

A philosophical thought for you:

So for the flashing LEDs, do you think it's most appropriate to operate them at the same speed as in real life, scaled down to the scale speed of the trains, or faster on the principle that the heart of a small animal beats more quickly than that of a large one?

Reply to
Andy Hall
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Maybe rather than KISS, make it complex... How's your software experience?, how's your son's?

One dead simple solution from the point of view of number of soldered connections would be to use a little PIC micro-controller; These can drive LEDs directly, and with sufficient software nounce you can get it to do whatever you need.

Could be fun for the sprog too (dunno if you mentioned his age?)

Regards

Reply to
Mike Dodd

I think it should be possible with one Tr but failing that an astable multivibrator will certainly do it.

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down for the circuit diagram, the good 'old 555 timer chip can perform this operation. Or you could buy a Brio level crossing that has two poles with alternate flashing LEDs, bell sound and gates that drop all triggered by the coupling magnets closing reed relays.

Reply to
Dave Liquorice

On Sun, 30 Jan 2005 09:08:43 +0000, Dave Stanton strung together this:

Sorry, I meant if the OP was after so simple it was simpler than simple itself you can get pre-made LED flasher units for bell boxes that flash alternately, which I think was at the end of the link, all you need to do is stick 12VDC on it and that's it.

Reply to
Lurch

snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel)

It was after my last post that I had that penny-dropping DOH! Moment. Works fine now, one flashing led, one ordinary led, one transistor, and two resistors, KISS !

Im building this level crossing for a 19-year-old nephew who is severely disabled after an accident, the mental and physical stimulus of operating a train layout is helping enormously in his recovery. Thanks for your help, and everyone else that took the time to reply.

Regards to all.

Reply to
F-Red

Surely a simple 2 transistor multivibrator (flip flop) with the leds in the loads would suffice, it would have the advantage that you could set the frequency and the mark to space ratio as you require. 2 transistors, 2 capacitors, 2 resistors, 2 leds(non flashing ) Cheers Tom

Reply to
Tom

Yup, could be fun...

I once had a ten page requirement spec come in from one of the bods on a hardware team (big defense contractor) to write software for a pair of flashing LEDs!

They had an azimuth and elevation meter, with a couple of analogue dials that indicated the position of a steerable turret under a helicoptor. They wanted an enhancement to have an LED flash when an endstop was reached on each axis. They had arranged to send a single byte command down a serial link to the meter, and then use a microcontroller in the back of the (small) meter to decode it and flash/light the required LEDs. Since they were short of space they used a "micropack" 8031 based controller, these where seriously expensive beasties (600 quid a shot at the time) with all the supporting circuitry and the 8031 all built on one substrate - just add power. Anyway, did the software for them (about

3 days work by the time all the documentation and QA stuff was done), and then to rub salt into the wound suggested an alternate design for the same functionality, using a hard wired UART, a PAL, and an astable at a total cost of under a tenner! (compared to what must have worked out at something getting on for 1.5 grand per LED, given the customer was only buying three meters!)
Reply to
John Rumm

Glad it works. If I'd had a flashing LED, I would have tried it before posting, but I don't;-) Incidently, if you're running it from a battery supply, the addition of a second transitor and resistor could knock a third off the current consumption.

Best of luck with it.

Reply to
Andrew Gabriel

"Tom"

Yes but I had already built the board to control the level crossing, with no spare room for adaptations. For simplicity sake I was going to use two flashing leds per signal post x4 until I realised that the flash timing looked unrealistic. So I had a space of about 5mm x 5mm within each post to birds-nest in something that worked, which this does superbly. And it scores higher on the KISSometer than any other design i've seen.

Reply to
F-Red

Got ya ! Dave

Reply to
Dave Stanton

On the subject of flashing LEDs, anyone know of a low power consumption slow flashing all in one? For a car burglar alarm where the existing one - built into an external sensor didn't flash, but the one I've fitted from IIRC Maplin is very bright with about a 50% duty cycle, but draws too much current on a car which isn't used every day. And there's no room inside the sensor to add any circuitry. Something like one flash every 10 seconds would be ideal.

Reply to
Dave Plowman (News)

I don't, nor does the RS catalogue: the integral-flasher types I see there all quote a consumption of give-or-take 40mA; galling when there are 'high-efficiency' LEDs pulling as little as 2mA, and a CMOS 555 could readily have high-value Rs and a 10microF tant to give the slow, low-duty-cycle flashing you want, if only there were room.

However, it's not clear to me that it's the LED which is the main culprit in your alarm discharging the rarely-charged battery - have you had a chance to measure the whole alarm's draw, with and without the LED connected? 40mA times 24hours would be 1AH, so a week's draw for the LED alone wouldn't be more than 7AH - which should be well within the realms of 'trivial' for a typical car battery of claimed 50-80AH. Maybe a little solar trickle-charger, or maximally-convenient way of connecting a mains lead-acid charger (with decent charging control), would meet the overall requirement?

Reply to
Stefek Zaba

Have a look on RS/Maplin for a flashing LED driver chip (8 pin DIP). I fitted one to my old Escort (old as in '85ish) as a deterant(*) flashes at about that rate but as a bright pulse, takes very little current as it charges a C which it then discharges through the LED.

LM3909 is the chip datasheet at:

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found by Maplin, RS, CPC or Farnell, discontinued due to age I suspect. B-(

(*) Probably worked, the car was stolen when the LED wasn't flashing for some reason...

Reply to
Dave Liquorice

"Dave Plowman (News)"

Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery.

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even if the car battery is being drained by something else and goes flat, the LED keeps flashing. I know you said "no room inside the sensor" but only two wires from led need to go into the sensor.

Reply to
F-Red

Snag is the LED is part of the motion detector assembly which has no spare room inside for extra components. The original was a non flashing very dim LED which I replaced with a very bright all in one with a 50% duty cycle. I'd prefer one just as bright, but a slower flash rate. The factory fit one on my other car flashes about every ten seconds.

Reply to
Dave Plowman (News)

Snag is the sensor mounting is hinged, and the cable goes through the hinge. Would be possible to change it for one with more cores, but difficult. And the sensor is mounted on a removable parcel shelf so is plugged in - that would have to be changed too. ;-)

Reply to
Dave Plowman (News)

and a C...

My thoughts as well, normally plenty of space behind trim panels. I don't think Dave will find a pulse type flashing LED, they generally need a decent sized C to store the charge, difficult to manufacture on a bit of silicon. B-)

Reply to
Dave Liquorice

Indeed - though there's no reason-in-principle that the little-bit-of-silicon couldn't have a relatively high-freq oscillator (so minimal C needed), a string of dividers, and finally a counter so as to light the LED on a 1:7, 1:15, or 1:31 duty-cycle...

Reply to
Stefek Zaba

But with a minimal C where does the energy for the pulse come from? These pulse flashers are just a few mS long at 40mA or more. The amount of light you get from the normal 10 or 20mA of just a few mS duration is pretty dim...

Reply to
Dave Liquorice

Shamelessly drawn from Vcc - I'm happily assuming I can draw the 20mA or so to light the LED load from the powerline, for the brief duration of the lit pulse, without having to accumulate the coulombs myself during the longer unilluminated period. I'm only solving the average current-draw problem with the shorter duty-cycle, not a cycle-long limited current-draw constraint...

Reply to
Stefek Zaba

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