counterled
Is it possible to use a common cathode resistor for all 10 LEDs with 4017 decade counter? I try it but only the first LED (output 0) lights up.
EDIT: I got it working. My wiring was wrong. I use a 9V battery power supply. I plan to cascade multiple 4017s (up to 10 of them) to a single LED sequence – so I may get 100 LEDs hooked to a single common resistor.
The MM5450 may do what you want.
34 outputs, serial fed, chainable.
Notionally 3 pins to drive (clock, data, latch) but can be driven with 1 pin if needed. Digikey $4.39/1 This one in DIP-40 but also available in LCC.
if this does not suit your need you need to provide a more complete description of your requirement.
Outputs are open drain, ie either on = low or off = float or open circuit.
Things regarding a high side switching of a voltage higher than the control voltage are not as simple as they seem.
Take for example the following circuit controlled with an Arduino I/O pin
When the I/O pin is LOW the voltage to the base will be 0, that means that the Vbe will be 9v and since it is >0.7v the transistor will be on.
When the I/O pin is HIGH the voltage to the base will be 5v, that means that the Vbe will be 4v and since it is >0.7v the transistor will also be on.
So basically that configuration can't work as a switch because the transistor will always be on.
In order to make a circuit like the above work properly you have to add a level translator that will actually drive the base with 0v and 9v (or whatever the collector voltage level is), a circuit like
One alternative of a working single transistor high side circuit is an emitter follower like
The problem is that in this case the emitter will follow the base voltage when the transistor is on so for 0 and 5v control voltage you will get 0 and 4.3v output irrelevant of the voltage connected to the collector (within transistor specs of course) which may ot may not suite your specific application.
Another alternative is to use a device like ULN2003/2803 but intended for high side switching. Such a device is UDN2981 which has 8 source drivers like the following and can be used as a high side switch controlled by TTL level logic.
Best Answer
Yes you can, however it will subject the 'off' LEDs to reverse bias. If you are using a 5V supply or less, worst case will only be a few volts, which virtually all LEDS are rated for.
If you are using a CD4017 on an 18V supply, you will be exceeding the reverse rating of most LEDs-- typically 5V or so-- (but it might still work).
Each 'off' LED sees the output drive voltage (typically close to the supply voltage) minus the forward voltage of the 'on' LED (typically 2-3V, or maybe 1V if the LED is an IR type).