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FRED circuit in MR - blinking LED

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FRED circuit in MR - blinking LED
Posted by Benjamin Maggi on Wednesday, August 30, 2017 11:44 AM

When I was younger I built a circuit found in Model Railroader for a flashing rear end device (FRED) that was powered by a 9v battery and had a potentiometer to control flash rate. It worked great, and I want to build another as an electronics project. However, I cannot locate the article in MR anymore.

I assume it was from 1988-1995, but a search of the online index didn't cause anything to jump out at me. Does anyone know of the article I am thinking of, or an online schematic for the circuit?

Thanks.

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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Posted by rrinker on Wednesday, August 30, 2017 6:12 PM

 Remember they are also (at least as often, maybe more so, since it is the proper technical name) EOTs. Anyway, February 1990 has one as part of an article on building Front Runner spine cars. About as simple as you get, LM3903 LED flasher IC, capacitor (size of which determines flash rate), and an LED. It runs off 1.5V, not 9V. May 1992 Symposium on Electronics repeats the same circuit.

 You can also build one using a 555 timer, slightly more complicated circuit but it's one of the basic circuits shown on almost any page that teaches about the use of a 555.

 What's REALLY crazy is that you can take the 40 pin CMOS microprocessor from my first computer and wire it so that it blinks an LED and it will use far less power than the LM3909 circuit. No programming, just hook certain pins together to make it do things, and one of the pins turns on and off at a steady rate.

 BTW, go here to search: 

http://www.olimpia.com:8084/SearchPage.html

It does a better job (usually) than the one here, and it covers all hobby magazines in case that elusive article you're thinking about was in RMC or Model RailroadING.

                             --Randy

 

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by Benjamin Maggi on Wednesday, August 30, 2017 7:42 PM

Thanks Randy. I like the one I built, as it used a pot to determine the flash rate. I wonder if maybe I found it in one of those old "Easy Electronic Projects for Model Railroaders" books. I will keep looking, though I pulled the EOT circuit you referenced from 1990.

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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Posted by Gaucho on Wednesday, August 30, 2017 10:10 PM
How about using a 0402 smd auto flashing LED? No flasher circuit is required. You can get 10 for under $9 and they come pre wired.
 
Moe Bursztein
 
P.S. for a couple more dollars you can add smd bridge rectifier to drive a dc-dc buck converter and then you can use truck power.
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Posted by rrinker on Wednesday, August 30, 2017 10:12 PM

 Here's one with a 555 with a potentimeter

http://www.next.gr/other-circuits/555-lm555-ne555-timer-circuits/LED-Flasher-with-555-l7876.html

I guess if you put it in a house car there's room. There's another even simpler than the LM3909 one, uses a different flasher IC that is in a 3 pin package (looks like a transistor). I doon;t think it needs any other parts besides the LED and a resistor. The really tiny commercial ones are self contained in a freight car truck - Evans Designs and Ring Engineering sell ones like that, witht he LED even contained in a small box that sits on the coupler like an actual EOTD.

                                     --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by richg1998 on Wednesday, August 30, 2017 11:27 PM

Last I knew, the LM3909 was out of production. Probably surplus companies.

Google eot fred circuits or lm3909.

I bought the Ring Engineering truck with EOT a few years ago. Also bought the matching unlit truck.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by rrinker on Thursday, August 31, 2017 6:50 AM

 There's a millioon of them on ebay, of course.

But they are too expensive - you can buy an 8 pin ATTiny85 microcontroller for half the price. Add power, an LED, and resistor and you can alter the basic Blink sketch for Arduino to change the flash rate all you want.

There's that segment that goes "a programmable microcontroller is SO much more complex than a simple flasher circuit" Yes, it is, way overkill - but the crazy thing is, it's the cheaper solution! Cheap microcontrollers are what did away with many specialty chips like the LM3909.

                            --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    January 2002
  • From: Loudonville, NY
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Posted by Benjamin Maggi on Thursday, August 31, 2017 9:17 AM

Thanks. I want to build it as part of my Master Model Railroader certification, so I can't just buy a premade circuit. I have plenty of ideas now... thanks all!

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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Posted by maxman on Thursday, August 31, 2017 11:27 AM

Build an End of Train Flasher, by Eric Mumper, January 1986???

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Posted by Benjamin Maggi on Thursday, August 31, 2017 11:57 AM

Sadly, my collection of MR goes back as far as 1988. However, I have read older ones so that might be it. Can anyone who has that issue check and see if the circuit included a POT and a 9v battery?

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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Posted by maxman on Thursday, August 31, 2017 1:00 PM

I checked.  No it does not.  It was built in two versions, one with a AA battery, and one with a 1.4 volt mercury cell (whatever that is).  Also used a LM3909 which Rich (above) says is no longer available.  Did not see a pot in the part list.

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Posted by maxman on Thursday, August 31, 2017 1:05 PM

Found another article. "An EOT for the Front Runner" by David Bontrager, February 1990.  I didn't look at the article, but if you don't have that issue I can go through my magazines.

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Posted by Benjamin Maggi on Thursday, August 31, 2017 1:54 PM

Thanks. I just copied the 1990 article this morning from my collection. Indeed the LM 3909 chip isn't made anymore but I found some Chinese ones on Ebay. No idea if they will work, but for $3 it might be worth a shot.

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

  • Member since
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  • From: Loudonville, NY
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Posted by Benjamin Maggi on Wednesday, September 20, 2017 9:49 AM

I am collecting the parts for this project (and sorely miss Radio Shack!) and discovered that the schematic printed in MR shows the LED itself as having the long leg as positive (+) and the short leg as negative (-). I always thought that it was the reverse. I don't know if the circuit was later corrected in MR, or even if it matters here.

I was going to wire it up per the polarity (+, -) and ignore the drawing which shows short and long legs. However, if I get it wrong will the LED blow up, will it just not light up, or might it destroy other components in the circuit? I bought a package of several LEDs so I don't mind wasting one if I do it wrong, but I don't want to risk damage to anything else.

Anyone know the answer to this?

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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Posted by rrinker on Wednesday, September 20, 2017 1:06 PM

 The standard is the long lead is +, the short one, also the side with the flat on the case if it's a 3mm or 5mm one is the -. Short, flat, cathode, - sign. 

Hooking up the LED backwards won't fry it, it just won't work.

                          --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    January 2002
  • From: Loudonville, NY
  • 772 posts
Posted by Benjamin Maggi on Thursday, September 21, 2017 9:28 AM

Thanks Randy!

Modeling the D&H in 1984: http://dandhcoloniemain.blogspot.com/

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