This circuit is for a "F.R.E.D." that is designed to be used with DCC control systems. The circuit is based on the LM555 timer chip.
Two versions of the circuit are shown. The first uses a full wave supply while the second uses a half wave supply. Both should work equally well.
The flash rate and duration can be adjusted by changing the values of the resistors R1 and R2 in the timing portion of the circuit.
Increasing the value of resistor R1 will slow the rate at which the LED flashes. Increasing the value of resistor R2 will lengthen the time that the LED is ON.
If a battery powered unit is desired the following circuit could be used. LM3909 Replacement Circuit
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.