555 Timer and DC motor

Thread Starter

jonnythain

Joined Jun 27, 2011
27
Hi,

I have a relay that controls a monostable 555 timer. The output of the 555 timer has 3 switches at the output that turn on a row of 4 led's, piezo buzzer and a DC motor. The circuit is configured to give 1.5 seconds at the output to operate each device similtaniously (can be switched on or off independently). The issue is i cannot seem to get the DC motor to pulse for 1.5 seconds (as it is just to provide a vibration, like the rumble in an xbox controller etc). The rating of the motor is:

Operating voltage 1.5 - 5Vdc.
Rated load 10 g.cm.
Speed@rated load - 5000rpm
Current@rated load - 450mA.
No load current - 130mA

The circuit runs from a 9V battery

Would i have to use a transistor and zenner diode? Any ideas woul dbe much appreciated.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
I seem to have another problem now. If i put my voltmeter accross Pin 3 and 0V i see the voltage for acout 1.5 seconds and then it goes back to 0V which is what i expect. When i use either by led or buzzer it switches on and doesnt go off??? It was working befor ei started messing with it, but i just cant understand why this is happening, it is as if if a current is being drawn from the 555 timer it stays switched on??? It was definitely workign with the buzzer and led before i started tampering to get the motor to work.

Thanks
 

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SgtWookie

Joined Jul 17, 2007
22,210
Your battery is probably getting quite discharged. PP3 9v "transistor" batteries don't last very long when you are putting so much power drain on them.

Also, you are probably overloading the output of the 555 timer. They are rated to source or sink up to 200mA (BJT versions); the CMOS versions can sink up to 100mA but only source 10mA.

Your motor would be way too much load for the 555 timer without at least 30 Ohms of resistance in series with it. 9v-5v/130mA = 30.7 Ohms.

I don't know what kind of LEDs you are using, but unless they had a Vf of 1.75v or less, they would not even light up when you have 4 in series.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
If we forget the motor part of it now, i still dont understand what is happening with the circuit. I have buitl the circuit and as i have said when the circuit is triggered all the LED's come on but they stay on permanently. Like i said this wasnt happening before, and is the same if i just attach the buzzer. If no current flows out of the 555 (i.e. using my voltmeter only) then the cirucit work correctly.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
I have since attached a sinle LED and current limiting resistor to the output. When i measure the output current it is about 4mA and once this flows it doesnt stop. If no current flows the 555 turns the output off after the time period i have chosen.

Please can someone tell me why thi sis the case as i have to give a presentation on Monday and i was all working this morning how i expected it to!
 

SgtWookie

Joined Jul 17, 2007
22,210
You need to start measuring voltages at the other pins when it is working properly, and then when it malfunctions.

Are you certain that pin 4 is connected to Vcc? If it gets pulled to ground, the timer will "stick" with the output high.

Take a clear photo of your project and post it. It can be difficult to get a clear photo. Many people try to take a picture too close so it's out of focus, and/or with poor lighting - those don't help us.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
Yes i am certain it is connected t Vcc. I have done what you said when the circuit is and isnt working (i.e. Voltmeter only attached or LED sting). The reasings are as follows:

Not working:

Pin 1: 0V
Pin 2: Goes to 0V then to 7.85V
Pin 3: 6.95V
Pin 4: 8.25V
Pin 5: 0V (also turns the LED's off when this connection is made)
Pin 6: 8.03V
Pin 7: 8.03V
Pin 8: 7.37V

Working:

Pin 1: 0V
Pin 2: Goes to 0V then to 8V
Pin 3: 7.45V
Pin 4: 8.21V
Pin 5: 5.21V
Pin 6: 5V
Pin 7: 5V
Pin 8: 7.45V

Cheers
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
Can i just add something i have discovered after seeing something strange on pin 5. I tried connecting a capacitor from pin5 to ground which seemed to make little difference. However if i attache a probe to pin5 with a crocodile clip on the other end and connect a probe to ground and crocodile clip on the other end and simply hold on to them the circuit works ok. If i let go it stops working and stays on again. Is it the capacitance of my body that is making thi work???
 

SgtWookie

Joined Jul 17, 2007
22,210
That's strange. Pin 5 is the control voltage pin. It should always measure 2/3 of Vcc (pin 8), in your case if pin 8 is 9v, it should measure 6v.

Your battery is measuring ~7.4v, which indicates that it is dead. You need a fresh battery.

Not working:

Pin 1: 0V (That's what it should be)
Pin 2: Goes to 0V then to 7.85V (It should go to 0v when button pressed, same as pin 8 when released)
Pin 3: 6.95V (This is the output; should be either ~pin 8 minus 1.3v or zero)
Pin 4: 8.25V (This should be the same as pin 8)
Pin 5: 0V (also turns the LED's off when this connection is made) [this should not be shorted to ground]
Pin 6: 8.03V (should measure same as pin 8 when cap C1 is charged)
Pin 7: 8.03V (ditto pin 6)
Pin 8: 7.37V (It looks like your battery is getting rapidly discharged.)

Working:

Pin 1: 0V - ok
Pin 2: Goes to 0V then to 8V - ok
Pin 3: 7.45V - ok
Pin 4: 8.21V - you must have made this measurement early.
Pin 5: 5.21V - ok, that's about 2/3 of pin 4, which is connected to pin 8
Pin 6: 5V - this must've been a momentary reading. Pin 6 & 7 should either measure same as 4 & 8, or be ramping up from 1/3 Vcc towards Vcc.
Pin 7: 5V - ditto pin 6
Pin 8: 7.45V - in the time it took for you to read from pin 4 down to pin 8, the battery discharged from 8.21v to 7.45v - or else you have a bad connection between the two pins.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
I am sure it is to do with PIN 5. I have since found the following:

Voltage on Pin 5:

When working

Before trigger: 5.46 V
On trigger: 5.52 V
After trigger timer period: 5.46V

Not working

Before trigger: 5.46 V
On trigger: Climbs to 8V
After trigger timer period: remians 8V
Manually break output LED circuit as failed to go off: 5.46 V

Any more ideas? This mornign it appeared to work for a period but has started doing the same again.

I appreciate the responses so far so thanks.
 

SgtWookie

Joined Jul 17, 2007
22,210
You probably have damaged your 555 timer by overloading it. The LEDs and piezo buzzer were OK, but the 1.5v to 5v motor was too much when powered by 9v.

If R1 is really 1.5k and C1 is 1000uF, I suggest that you instead use 150k for R1 and 10uF for C1, or 15k for R1 and 100uF for C1. The timing works out the same, but you will dissipate a lot less power in R1 when pin 7 is discharging C1.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
Hi i thought about that so i changed my resistor to 24k and used a 47uf capacitor. It work and when it seeme dto stop i tried resoldering the cpacitor and seemed to fix it for a a short period. Im just wondering if im shorting something which is resetting the timer???
 

SgtWookie

Joined Jul 17, 2007
22,210
If you short pin 4 and 5 together, you will see CTRL go to Vcc, as pin 4 is usually tied to Vcc. Pins 4 and 5 are on opposite sides of the IC, so you would kind of have to work at it to do that. If you are working on a breadboard and have long, bare leads on components and long, loopy jumpers, this scenario becomes much more likely.

You could also wind up with problems if 5 and 6 were shorted; this would be very easy to do, as they are right next to each other.
 

Thread Starter

jonnythain

Joined Jun 27, 2011
27
I think i have found the issue, i have a felling as i connected Pin 2 via a wire to another wire on one half of the trigger switch that they were somehow loose connections. So i think it was my trigger that may have been triggering and staying on, but it doesnt expalin the other readings (or does it) could a bad trigger/one half of switch be casuing the problem?
 

sheldons

Joined Oct 26, 2011
613
ive rearranged your circuit a little and added a driver for your motor,leds and buzzer.have decoupled pin 5 and added a switch debounce circuit to prevent false triggering(supply for the 4093 is pin 14(+v) and 7(gnd)
 

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