I’m designing a simple SW receiver for the 20m band and need a rudimentary frequency indicator activated by the multiturn rotary knob. The knob is part of a recuperated Pritt gluestick mechanism pushed into service as a PTO-drive for the VFO. The idea is to use reed switches to power the indicator LEDs on the frontpanel. On the glueholder a stick is glued which holds a magnet at the end. As the knob is turned, the magnet advances over 6 reed contacts, each in turn activating a corresponding LED on the frontpanel. Of course, as soon as the magnet is advanced, the active LED is switched off and there is no indication for the duration of the next cycle until the next LED is turned on. Is there a way to make it so that the last LED remains lightened until the next is switched on? Of course this also need to work in reverse. Thanks beforehand for your help!
You are trying to describe a very Rube Goldberg type of mechanism for something that should be done in a much more uncoupled manner. You should come up to speed what microcontrollers are all about. Have the microcontroller (MCU) able to detect position of the knob (which can now be a simple potentiometer feeding an A/D converter OR a rotary encoder feeding quadrature waveforms to two inputs). The MCU would also control the display and run the VFO. You tie all this together with software that can easily solve the problem of when the display should change in relation to how the rest of the things change.
For each reed switch you need a D type latch and specifically you need a D type latch that has a clear pin. For all D type latches you wire the "D" inputs to logic 1. For the D latch that is directly associated with a particular reed switch, the reed switch feeds its clock input.
This means that one side of the reed switch is tied to logic 1 and the other side that connects to the clock has a (typically) a 1 kohm to 10 kohm pull-down resistor.
That clock input also connects to the other D latch clear inputs via individual diodes to each clear pin. Ensure that there is a pull-down resistor on each clear input.
Step and repeat for all reed switches and D latches.
Or just use a microcontoller and software to control the LEDs