This is a simple little project I have been working on, intended to flash LED's for road crossing flashing lights. The circuit as shown alternately flashes the LED's at about 2 seconds for a complete cycle, which looks about right to me. The cycle length can be lengthened by increasing the values of either C2/C3 or R3/R4. But I would like to be able to adjust the cycle length on the fly without the bother of changing components. I could put individual trimmer pots in place of R3/R4, but is there a simpler way to do this? I know there is a board available at wehonest which includes variable flash speed, but I kind of want to build my own. Thanks for any help.