I have a SP4T slider switch, where common is connected to the power rail and each pin is connected to a led and resistor. The problem is, if I position the switch between two terminals, the leds of both terminals light up. Is this a sign of a bad switch? Even if it is, are there any way to prevent two leds lighting up at the same time with this switch?
Electronic – SP4T slider switch on two states at the same time
ledswitchestoggle switch
Related Solutions
You can simply use your 4 position switch to generate a control signal that then switches control elements (like MOSFETs). You need to change your LED drives to this (note I only show one LED and One switch)
simulate this circuit – Schematic created using CircuitLab
Something similar can be done with the 555 as well,
Of course signal ctrl2, 3 etc. is not shown.
the main concern with this approach is two fold.
1)you must ensure that the gate swing is large enough that the transistor is remains fully conductive over the whole operational range.
2) if you put too large of a MOSFET in there the stray capacitance on the resistor chain will change the operating conditions.
Add a diode in each lead from the buzzer to the collector of the transistor (in that direction).
Current can flow through a diode in one dircetion only (the 'arrrow' direction) so it can flow from Vcc through the buzzer and a diode to one of the transistors and to ground, but not from one LED to the other transistor, because one of the diodes would block it.
An 1n4148 will do up to ~ 100 mA, otherwise pick an 1N4004. (or any other 1n400*)
PS your opamps feed the base of the transistors directly. Unless it is a current-output opamp (in which case the circuit would not work as expected) this is not a good idea. Put resistors in series with each base, 10k will probably do.
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Best Answer
Not necessarily. Switches come in "make before break" and "break before make" variations.
In some applications it might be desirable to always have the common connected to something rather then let it float. e.g. When switching between two audio sources it may be better to short them together rather than have the audio floating during transition and picking up a hum. Use "make before break".
In other applications it may be undesirable to have a short. Use "break before make".
Even if it is, are there any way to prevent two LEDs lighting up at the same time with this switch?
Not easily. You haven't shown your circuit. There may be some means of doing it.
Figure 2. A typical low-cost 4-position switch.
If the switch is of the type shown above you should be able to open it by unfolding the metal tabs underneath. Examine the contacts and see if you can file away enough between them or modify the wiper contact carefully to change it into a break before make. Obviously, this would be best attempted on a spare switch.