In the very popular article in the March 2001 issue of Model Railroader on simple automatic 3 light block signals by Jeff Scherb Figure I on the resistor values for 12 volt positive anode led`s does not agree with the electronic circuit diagram. Can you tell me if this is a misprint? I looked at the fol;lowing 2 issues and did not see a retraction of the values. Thanks
Bob D As long as you surface as many times as you dive you`ll be alive to read these posts.
Be more descriptive. What do you mean, does not agree with the circuit diagram?
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.
although there is a specific 'correct' value for a resistor ( different colour LED's from the same manufacturer can have different value resistors ) aslong as you are in the ball park things will work ok, but the colour won't be quite the same as it would be with the 'correct' resistor.
http://home.cogeco.ca/~rpaisley4/LEDcalc.html
Rich if you have that issue of MR look at the circuit diagram for the 12 volt system. It shows that the value of R1 is 470 ohms and R6 is 1K ohms. The resistor values shown in table 1 for a 12 volt system show just the opposite values. Table 1 has R1 at 1K ohms and R6 at 470 ohms for a 12 volt system.I hope iv`e been descriptive enough to explain the problem.
RF&Prr I`d like to thank you for that website.I have made a copy of it for future reference. I will be using his circuit for the signal current detectors. It has far fewer components than Bruce Chubbs circuit , although I like Bruces sensitivity control on his circuit with the 10K pot. & the LED .
submanRich if you have that issue of MR look at the circuit diagram for the 12 volt system. It shows that the value of R1 is 470 ohms and R6 is 1K ohms. The resistor values shown in table 1 for a 12 volt system show just the opposite values. Table 1 has R1 at 1K ohms and R6 at 470 ohms for a 12 volt system.I hope iv`e been descriptive enough to explain the problem.
My mistake. I was looking at the second part in the April issue. Apparently, no one ever questioned the article/author or contacted MR magazine editor.
I have worked with circuits like this for many years and the values in the March issue of 470 and 1k are ok. Red LED's tend to be brighter than green and yellow LED's and the 1k lowers the brightness of the Red LED. At least that is my experience in using LED's for model railroad signals. Other than that, the brightness issue has never occurred to me.
I have made single target signals using Red/Green bi-polar LED's and the Red is always brighter than the Green when the polarity to the LED changes.
Usually LED specs call out the brightness of the LED and you can plan accordingly.