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I'm trying to figure out how to make in the below schematic, LEDs D2, D3, and D4 blink respectively while the LM3914 is in dot mode when their on state occurs. Basically this would act like a warning indicating that you should recharge soon, and D1 would just be solid on when it's respective on state occurs (dot mode). I would like to do this with no 555 timer or micro controller either, using as few components as possible. Edit: I'm using a 10 segment LED bargraph.

enter image description here

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  • \$\begingroup\$ Have you considered using blinking LEDs? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Oct 19, 2014 at 3:18
  • \$\begingroup\$ No, I'm using a 10 segment LED bargraph \$\endgroup\$
    – klcjr89
    Commented Oct 19, 2014 at 3:20
  • \$\begingroup\$ So, to be clear, it's in dot mode, and you want to make all three LEDs flash simultaneously? \$\endgroup\$
    – Connor Wolf
    Commented Oct 19, 2014 at 3:40
  • \$\begingroup\$ Not at all, only one LED will flash at any time; what I want is D2, D3, and D4 to flash when their given state is on. And yes, it will be in dot mode. Also note that this is a stock 10 segment LED bargraph. \$\endgroup\$
    – klcjr89
    Commented Oct 19, 2014 at 4:15
  • \$\begingroup\$ Why the no-555 nor-µC requirement? \$\endgroup\$
    – jippie
    Commented Oct 19, 2014 at 5:22

1 Answer 1

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You can use the flashing bar display circuit shown in the LM3914 datasheet (figure 20). To have multiple flashing LEDs in dot mode you just have to add a diode between the timing capacitor and each output that you want to flash.

enter image description here

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  • \$\begingroup\$ What is R1, R2, and R3 for? \$\endgroup\$
    – klcjr89
    Commented Oct 19, 2014 at 13:01
  • \$\begingroup\$ They increase voltage swing at the LED outputs (which is required to make the flashing circuit work) and limit the flashing current. For working on 12V you may need to experiment with resistor values. I got good results with R1-R3 = 330 Ohms, R4 = 2k2 and R5 = 1k. I also added a 330 Ohm resistor in series with LED1, as it flashes when the input voltage is halfway between the 1st and 2nd levels. For consistency you might want to consider flashing LEDs 1-3 rather than 2-4 (that way the user knows that any LED flashing means low voltage). \$\endgroup\$
    – Bruce Abbott
    Commented Oct 19, 2014 at 19:17
  • \$\begingroup\$ Any way to not limit the current of LED2 - 4? I don't want them to be dimmer. \$\endgroup\$
    – klcjr89
    Commented Oct 19, 2014 at 19:32
  • \$\begingroup\$ The flasher circuit modulates the reference voltage and upsets the internal current limit. Without resistors, flashing LED current is limited to the maximum that the chip can produce. With the resistor values I used the flashing LEDs are actually a bit brighter than the static LEDs, which I prefer because I want them to be more visible. \$\endgroup\$
    – Bruce Abbott
    Commented Oct 19, 2014 at 19:41
  • \$\begingroup\$ Thank you for the help. About to post another LM3914 related question so be on the lookout for that :) \$\endgroup\$
    – klcjr89
    Commented Oct 19, 2014 at 19:45

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