A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.
PS I know there are lots of methods of doing this from ic555 ic4011 or even
two transistor oscillators, but that's not KISS enough for me.

On Sat, 29 Jan 2005 20:17:11 GMT, "F-Red"
wrote:

A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.
PS I know there are lots of methods of doing this from ic555 ic4011 or even
two transistor oscillators, but that's not KISS enough for me.

There's (was?) a dedicated LED flasher chip, the LM3909. Dead simple
to use!

Frank Erskine
MJBC, OETKBC

In article ,
Frank Erskine wrote:
There's (was?) a dedicated LED flasher chip, the LM3909. Dead simple
to use!

Or a voltage regulator, like the LM78

--
*Caution: I drive like you do.

Dave Plowman London SW
To e-mail, change noise into sound.

F-Red wrote:
I had hoped to use one flashing led to drive another ordinary led.

No chance, I'm afraid: the electronics do do the flashing are all sealed
up inside the body of the flashing LED; even when it's not flashing,
it's wanting to draw a little bit of current for the flashing circuit,
so you can't just put an ordinary LED in series with a flashing one and
expect it to light up in 'sympathy' with the flasher.

You'll just have to bite the bullet and knock up the simplest 555 timing
circuit you can (very few external components needed: two resistors, one
capicitor, one more capacitor for glitch-free running). A super-simple
circuit diagram appears at
http://www.hilaroad.com/camp/projects/electron5.html

and Googling with "555 flasher" throws up hundreds of similar ones.
You'd put your two LEDs, each with their own current-limiting resistor,
where these circuits show a single LED, if you want them both flashing
ON at the same time.

What about
http://www.kpsec.freeuk.com/proj.htm
http://wild-bohemian.com/electronics/flasher.html
http://ourworld.compuserve.com/homep...n/homepage.htm

"F-Red" wrote in message
4...
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.
PS I know there are lots of methods of doing this from ic555 ic4011 or
even
two transistor oscillators, but that's not KISS enough for me.

PS I know there are lots of methods of doing this from ic555 ic4011 or
even two transistor oscillators, but that's not KISS enough for me.

Maplins do/used to do, a 2 x transister flashing led kit. Used one for my
outside alarm box.

Dave

--
For what we are about to balls up may common sense prevent us doing it
again
in the future!!

In article ,
"F-Red" writes:
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.

What happens if you connect a flashing LED in series with an
ordinary LED? Maybe the off-state current is still enough to
light the other LED?

Also, what supply voltage to you have to hand, and do you
know the part number of the flashing LED?

--
Andrew Gabriel
Consultant Software Engineer

In article , Andrew Gabriel
writes
In article ,
"F-Red" writes:
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.

What happens if you connect a flashing LED in series with an
ordinary LED? Maybe the off-state current is still enough to
light the other LED?

I think you have the right idea andrew, a quick look at some flashing LED
data shows some latitude in the supply voltage (9-12V) so should work
from a 12V supply with an LED in series. A resistor in parallel with the
slave LED will allow some quiescent flow without it lighting, 1k would let
1mA flow w/o any risk of lighting. 20mA seems to be a typical ON current.

A possible problem is that the flasher chip will see its voltage change from
~10 when both LEDs are on to ~12 when both are dark which may upset
it, so it is one to suck and see. Other risks are intensity, spread & colour
matching.
--
fred

F-Red wrote:
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.

Should work.
You connect the flashing LED in series with the ordinary one (it'll need
2-4V (red-blue) more to work.

What happens?

Ian Stirling

F-Red wrote:
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two
flashing leds together as the flash rate and sequence is wrong, so I
had hoped to use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.

Should work.
You connect the flashing LED in series with the ordinary one (it'll
need 2-4V (red-blue) more to work.

What happens?


Thank's for everyone replies, but the LEDs have to flash in sequence, one
on other off.
Just like on a real crossing !
I had hoped to do this with *ONE* transistor, ie bias for base being
supplied by resistor/ Flashing led junction. But that don't work because
they both flash together.
I shall have to go to bed tonight and dream about this, that always
provides a solution.

In article ,
"F-Red" writes:

Thank's for everyone replies, but the LEDs have to flash in sequence, one
on other off.
Just like on a real crossing !
I had hoped to do this with *ONE* transistor, ie bias for base being
supplied by resistor/ Flashing led junction. But that don't work because
they both flash together.
I shall have to go to bed tonight and dream about this, that always
provides a solution.

Ah -- I was thinking you wanted them on together.
Try something like this:

+ve ----------------
| |
| /
--- \
\ / flasher / 680 ohms
--- \
| |
| ------
| NPN | |
| |/ |
|------| ---
| |\| \ / LED
/ -| ---
100 \ | |
ohms/ | |
\ | |
| | |
| | |
0v --------------------

Any small low gain NPN transistor should do here
which can handle, say, 20mA base current, e.g.
BC635, BC639 (or BC546, BC547 but their gain is
a bit high). If the separate LED does not switch
right off, reduce the value of the 100 ohm resistor.
Adjust the 680 ohm resistor if the two LEDs are
different brightness.

--
Andrew Gabriel

In article ,
(Andrew Gabriel) writes:

Any small low gain NPN transistor should do here
which can handle, say, 20mA base current, e.g.
BC635, BC639 (or BC546, BC547 but their gain is
a bit high). If the separate LED does not switch
right off, reduce the value of the 100 ohm resistor.
^^^^^^
meant to say "increase"

Adjust the 680 ohm resistor if the two LEDs are
different brightness.

Actually, try reducing 100 ohm resistor first if
it needs brightening. If doing this stops the LED
switching right off or you want to dim the LED,
then try adjusting the 680 ohm resistor.

Without a datasheet for the flasher, I can only
guess what its on and off currents are, hence
the need for playing with the values.

--
Andrew Gabriel

(Andrew Gabriel)

In article ,
"F-Red" writes:

Thank's for everyone replies, but the LEDs have to flash in sequence,
one on other off.
Just like on a real crossing !
I had hoped to do this with *ONE* transistor, ie bias for base being
supplied by resistor/ Flashing led junction. But that don't work
because they both flash together.
I shall have to go to bed tonight and dream about this, that always
provides a solution.

Ah -- I was thinking you wanted them on together.
Try something like this:

Hmm that's were I started :-?
Current flows to tr/base when flashing led is ON ;-(

In article ,
"F-Red" writes:
(Andrew Gabriel)

In article ,
"F-Red" writes:

Thank's for everyone replies, but the LEDs have to flash in sequence,
one on other off.
Just like on a real crossing !
I had hoped to do this with *ONE* transistor, ie bias for base being
supplied by resistor/ Flashing led junction. But that don't work
because they both flash together.
I shall have to go to bed tonight and dream about this, that always
provides a solution.

Ah -- I was thinking you wanted them on together.
Try something like this:

Hmm that's were I started :-?
Current flows to tr/base when flashing led is ON ;-(

Indeed, which switches the other LED off.

--
Andrew Gabriel

On Sat, 29 Jan 2005 23:46:15 GMT, "F-Red"
wrote:

Ian Stirling

F-Red wrote:
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two
flashing leds together as the flash rate and sequence is wrong, so I
had hoped to use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.

Should work.
You connect the flashing LED in series with the ordinary one (it'll
need 2-4V (red-blue) more to work.

What happens?


Thank's for everyone replies, but the LEDs have to flash in sequence, one
on other off.
Just like on a real crossing !

Do you have barriers that come down in sequence as well?


I had hoped to do this with *ONE* transistor, ie bias for base being
supplied by resistor/ Flashing led junction. But that don't work because
they both flash together.
I shall have to go to bed tonight and dream about this, that always
provides a solution.

That could produce a short circuit....




--

..andy

To email, substitute .nospam with .gl

Andy Hall

Thank's for everyone replies, but the LEDs have to flash in sequence,
one on other off.
Just like on a real crossing !

Do you have barriers that come down in sequence as well?

Oh yes, and a little amber Led that comes on first, triggered by an
approaching train.

On Sun, 30 Jan 2005 00:56:07 GMT, "F-Red"
wrote:

Andy Hall

Thank's for everyone replies, but the LEDs have to flash in sequence,
one on other off.
Just like on a real crossing !

Do you have barriers that come down in sequence as well?

Oh yes, and a little amber Led that comes on first, triggered by an
approaching train.


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?



--

..andy

To email, substitute .nospam with .gl

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



"F-Red" wrote in message
. ..
Andy Hall

Thank's for everyone replies, but the LEDs have to flash in sequence,
one on other off.
Just like on a real crossing !

Do you have barriers that come down in sequence as well?

Oh yes, and a little amber Led that comes on first, triggered by an
approaching train.

On Sat, 29 Jan 2005 23:46:15 GMT, F-Red wrote:


Thank's for everyone replies, but the LEDs have to flash in
sequence, one on other off. Just like on a real crossing !
I had hoped to do this with *ONE* transistor,

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

http://www.play-hookey.com/digital/e...l_astable.html

Scroll 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.

--
Cheers
Dave. pam is missing e-mail

"F-Red" wrote in message
4...
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds.
Iv'e got some flashing leds and some ordinary ones, cant use two flashing
leds together as the flash rate and sequence is wrong, so I had hoped to
use one flashing led to drive another ordinary led.
But ^&%^&% if I can make it work, if anyone can come up with a simple
solution I would be most grateful.
PS I know there are lots of methods of doing this from ic555 ic4011 or
even
two transistor oscillators, but that's not KISS enough for me.

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

"Tom"


PS I know there are lots of methods of doing this from ic555 ic4011
or
even
two transistor oscillators,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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


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.


--
F-Red

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.

--
*If all the world is a stage, where is the audience sitting?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
On the subject of flashing LEDs, anyone know of a low power consumption
slow flashing all in one?

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?

On Mon, 31 Jan 2005 10:07:02 +0000 (GMT), Dave Plowman (News) wrote:

Something like one flash every 10 seconds would be ideal.

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.

google LM3909 is the chip datasheet at:

http://www.solarbotics.net/library/d...ts/default.htm

Not 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...

--
Cheers
Dave. pam is missing e-mail

In article om,
Dave Liquorice wrote:
Something like one flash every 10 seconds would be ideal.

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.

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.

--
*Gaffer tape - The Force, light and dark sides - holds the universe together*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)"

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.


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.
http://discovercircuits.com/PDF-FILES/1vled3.pdf
so 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.

--
F-Red

In article ,
F-Red wrote:
I know you said "no room inside the sensor" but only two wires from led
need to go into the sensor.

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. ;-)

--
*If they arrest the Energizer Bunny, would they charge it with battery? *

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote:

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.
http://discovercircuits.com/PDF-FILES/1vled3.pdf

All those parts... the LM3909 t run from 12v has just the chip, 2 Rs,
and a C...

I know you said "no room inside the sensor" but only two wires from
led need to go into the sensor.

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-)

--
Cheers
Dave. pam is missing e-mail

Dave Liquorice wrote:


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.


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...

On Mon, 31 Jan 2005 19:47:03 +0000, Stefek Zaba wrote:

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...

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...

--
Cheers
Dave. pam is missing e-mail

"Dave Liquorice"

On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote:

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.
http://discovercircuits.com/PDF-FILES/1vled3.pdf

All those parts... the LM3909 t run from 12v has just the chip, 2 Rs,
and a C...

Er but the 3909 has been obsolete for at least 3 years, you can still get
them though.
$14 plus postage.
You could buy a new Fng alarm for that. !


--
F-Red

On Mon, 31 Jan 2005 23:09:40 GMT, "F-Red"
wrote:

"Dave Liquorice"

On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote:

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.
http://discovercircuits.com/PDF-FILES/1vled3.pdf

All those parts... the LM3909 t run from 12v has just the chip, 2 Rs,
and a C...

Er but the 3909 has been obsolete for at least 3 years, you can still get
them though.
$14 plus postage.
You could buy a new Fng alarm for that. !

I have a load of LM3909s. In fact a chip just fell to the floor from a
"bookshelf" in the living room - it was a 3909 :-)

--
Frank Erskine
Sunderland

In article , F-Red
wrote:

PS I know there are lots of methods of doing this from ic555 ic4011 or even
two transistor oscillators, but that's not KISS enough for me.

Standard building block bistable circuit will do what you want. Two
transistors, two capacitors and four? resistors.

--
AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems
http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk

Andy Luckman (AJL Electronics) wrote:

In article , F-Red
wrote:

PS I know there are lots of methods of doing this from ic555 ic4011 or even
two transistor oscillators, but that's not KISS enough for me.


Standard building block bistable circuit will do what you want. Two
transistors, two capacitors and four? resistors.


Hoew about a unijunction with the LED in its collector?

In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?
(I think it's about 30 years since I last used a UJT, and
that was to generate a timebase for an oscilloscope I was
building from an old telly;-)

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?
(I think it's about 30 years since I last used a UJT,

And that was probably 5-10 years after they stopped making them :-)

In article ,
"Mike" writes:

"Andrew Gabriel" wrote in message
...
In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?
(I think it's about 30 years since I last used a UJT,

And that was probably 5-10 years after they stopped making them :-)

Oh have they? How sad.
....and I still remember the part number I used - 2N2646

--
Andrew Gabriel

Mike wrote:

"Andrew Gabriel" wrote in message
...

In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?
(I think it's about 30 years since I last used a UJT,


And that was probably 5-10 years after they stopped making them :-)


I thought that a very short pulse every few seconds was what was required.

Don't use teh gate, use the (drain? No that's a FET surely...)

(Andrew Gabriel)

In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?

Just to be pedantic its E,B1,B2 on a UJT,Its an electronic switch, no gain
so no collector or drain :-)
It would work, but to be effective would need anther transistor, which
would make the component count as high as an ordinary flip/flop.

--
F-Red

F-Red wrote:

(Andrew Gabriel)


In article ,
The Natural Philosopher writes:

Hoew about a unijunction with the LED in its collector?

It would be hard (maybe impossible) to get the on-off ratio
50%. Also, the with the output being saw-tooth rather than
square wave in a conventional unijunction oscillator, the
LED would fade off each time. BTW, there's no 'collector'
in a unijunction transistor -- I presume you mean the drain?


Just to be pedantic its E,B1,B2 on a UJT,Its an electronic switch, no gain
so no collector or drain :-)
It would work, but to be effective would need anther transistor, which
would make the component count as high as an ordinary flip/flop.


I thought that the anode went into heavy conduction durng the pulse
discharge phase.