I need this circuit to pulse an LED while running a buzzer motor for an adjustable period

RV1 and C1 should give me 1 - 5s of pulse, while RV2 and C2 should adjust the LED ramp times

The LED will be a strip of up to 10 white LEDs

Will the 555 drive these transistors, or do I need a third transistor to drive both of them, or would mosfets work more effectively?


555 monostable led and motor circuit

  • \$\begingroup\$ also, is it necessary to have a 10nF cap on pin 5? \$\endgroup\$ – Dillon MacEwan Apr 8 '19 at 13:35
  • \$\begingroup\$ How much current will the LEDs and motor require? Also, please provide a link to the manufacturer's data sheet for the transistor and timer IC that you plan to use (there are many variants of the 555 timer). How much "ramp time" do you need? \$\endgroup\$ – Elliot Alderson Apr 8 '19 at 14:19

There are too many problems with this design to suggest a quick fix.

The biggest problem ( all of you should learn) is making a design without a list of measurable specs!

For example:

  1. 10 White LEDs require _2x10?mA at Vf=...3.1x2?
    • in a configuration of __?_ 5P2S ? parallel:series
  2. Haptic Motor has a DCR of ___ Ohms and avg current is __ mA @ __V
  3. Motor 1-shot time T1=__sec
  4. LEDs ramp up (linear?) with T2= ___
  5. The usable battery Voltage is 9.2V to ___ 7v? with capacity of ___mAh ?
  6. Battery life ___ ? cycle operations minimum using Alkaline.

The Motor DC resistance implies surge current V/DCR on startup and thus switch Rce=coll.Emit.equiv resistance

Rce= Vce(sat)/Ice for Ib= 5% to 10% of Ic=V/DCR

So LEARN how to write a simple spec

If you make it look like a datasheet table of parameters, bonus

  • list all important measurable, testable, acceptance criteria with tolerances preferably or min max.

  • Then if your design meets spec, it's perfect.

  • if not, add to change the spec. ( e.g. cost, construction, effort, environmental stress conditions... until done. )

Then it's perfect.

If certain components must be used, include datasheet link but only as a last resort, there may be better choices.

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