Electronics Questions & Answers ← browse Q&As

I am using LEDs as an example but the load will vary, such as a combo of LEDs and motors. I want to use the same voltage source(3.7V battery). At any given time, only one load is in use but the deciding factor is the combinations of switches selected. Depending on the path to theload, yes, there will be resistors added to my circuit but I would like to remove the push buttons and replace them with bjts. I am open to any suggestions.

I assume that you could use two "latching switches" each one giving you either a LOW either a HIGH (so it can give you 4 states), then you could use a multiplexer such as a CD405xB. to open one analog circuit (or two, with the CD4052B. But since the output is limited to 10mA (not really enough to light up brigthly a LED) but probably enough to turn on any NPN (the exact one depend on the POWER than can dissipate and the VOLTAGE it can block, as example, an NPN for a LED is probably not right for a 12V DC MOTOR).

For the datasheet of the CD405xB, from TI, see CD405xB, more precisely, at its page 18, section 8.4, Table1.

You can look for any "Multiplexer IC", at Mouser, Digikey, etc. Your choice. Doesn't need to be analog output, in this case, as I undersand it, mainly if you add other NPN to control each of the 4 sub-circuits.

If you have another way to instruct your circuit which sub-circuit must be turned on (assuming only one of 4 could be), please, elaborate a little bit more.