Old post (circuit) problem

[myp71]

I have a problem with a circuit that was previous built circuit that I built off the n&v forum.This circuit was designed to beep when I put on the parking brake on my truck but lately it has been beeping when the ignition switch is turned off.This creates a problem because it beeps all of the time if the brake is on or off <p>What whould be a simple way of fixing this problem with out re-doing this circuit. <p>This is the link and the circuit was done by David Bridgen<p>http://206.131.241.58/ubb/ultimatebb.ph ... 1&t=001009<p>[ December 05, 2003: Message edited by: my p71 ]</p>

[dyarker]

Does the dash board light that you tapped off still work? If the bulb is burned-out, your circuit is only "seeing" 0 Volts on input that is open or short depending brake position.<p>Or, the wire from the lamp to your circuit has worn insolation and is grounding somewhere.<p>Or, the transistor driving the chime has an emitter collector short. Replace it. If you are driving the chime directly with the 555, modify the circuit with a one transistor buffer, and replace the 555.<p>Can you send me a schematic? Troubleshooting is much easier that way. .bmp is OK, but .gif or .png are better. I can use .dxf from CAD programs too.<p>C U L

[myp71]

Hi <p>sorry I do not have a circuit digram but I do not know if you went down that far on the link but the info on the post # 11 down from the top might help because that's what I went off of to build the circuit.<p>
<p>Dash board light still works.<p>Also so more info that might help <p>I added one of thoes little voltage reducers on the circuit so it gives 12v to the voltage reducer then from the voltage reducer it goes out to the( @1.5volts) beeper driver circuit (from an old alarm clock)
the voltage reducer is one of thoes ready made plug-in to your car 12volt cig lighter then you can adjust the voltage coming out of the voltage reducer<p>[ December 05, 2003: Message edited by: my p71 ]</p>

[myp71]

Do you think that I should replace it with a transistor buffer and replace the 555 timer?<p>what is a transistor buffer?

[dyarker]

A 555 won't work from 1.5V. The wife has hidden my 555 Cookbook; but I think the max Vcc range is 4.5V to 18V, with best results at 10V to 15V.<p>So now I think the problem is the supply voltage. Change back to 12V battery.<p>To prevent the 1.5V alarm clock beeper from burning up, put a resistor between it and pin 3 of the 555. You didn't say how much current the beeper needs, so I can't give you a value. At around 10mA, a 1.2K Ohm 1/4W; at around 20mA, try 500 Ohms 1/4W; 50mA 200 Ohms 1/2W; etc.<p>The 555 may, or may not, be bad. ICs in general don't like input pins with a higher voltage than the supply pin(s). In this case, pin 2 to 12V dash, compared to 1.5V on pins 4 and 8. The 555 may be okay because the series capacitor on pin 2 allows only pulses of 12V, and 555s are pretty tough.<p>You don't need a buffer (AKA driver) unless the beeper draws more than 150mA (unlikely). ((At the link, David says "up to 200mA"; and a rule-of-thumb for design is to use only 50% to 75% of a device's max rating.))

[dyarker]

Re: "What is a buffer?"<p>When load power required is greater than available power out of a controller, a buffer or driver cicuit is needed. Basically an it is an amplifier, but not usually called that in ON|OFF situations.<p>For example:<p>Let's say your beeper for this project uses 100mA. A 555 can handle upto 200mA, so no sweat, connect it directly.<p>Maybe for your next project you want to use a 555 to flash the head light high beams like police cars. You find a heavy duty relay to control the lights, but it's coil needs 600mA. Add a resistor and a 2N2222 between pin 3 and the coil, and you've built a relay driver or buffer circuit.<p>No big deal, just terminology.<p>To stretch the example, use a CMOS 7555 for the head light thing. And let's imagine that the max current on pin 3 of a 7555 is 5mA. It may not work because specified minimum gain for 2N2222 is 100. 600mA divided by 100 is 6mA; 1mA too much. One way to fix this is to double buffer with a 2N3904. (pin 3 to 2N3904 to 2N2222 to relay to lights)<p>Sorry is this sounds like baby-talk to you. No insult intended. I tried to write it so beginning beginners can understand too.<p>C U L

[myp71]

Thanks Dale Y for the help in terms that I can figure out. <p>The timer circuit power is 12volts input then from the timer circuit output goes the voltage reducer then to the beeper so the 555 is seeing 12volts.<p>so it might be another problem I'm having on the circuit Right?? <p>One thing I can not understand this timer circuit does not have the ground applied until the parking brake is applied so where is the power going to make the beeper beep without a ground?<p>Do I only get these strange happenings??

[myp71]

Dale
myp71<p>[ December 08, 2003: Message edited by: my p71 ]</p>

[dyarker]

No ground??

[myp71]

Yeah when the parking brake is not on(no ground) and when I turn off the ignition the beeper beeps I have it so the circuit gnds out through the parking brake switch and circuit power (12v)+ is going to a hot all the time inside the truck so without a ground how can the beeper beep??

[myp71]

Do you think that when the battery from the truck goes down from 13.6volts, then when I turn off the truck the battery goes to say 12.5volts thats when the beeper is activated some how by that change in voltage from when the engine is turned off?But the circuit still does not have a ground anywhere!Maybe the voltage positive side needs to be filtered some how so when the parking brake is not on and when I turn off the truck the circuit does not beep until the brake is on.<p>(sorry for such a long and drawn out post)

[dyarker]

Thinking

[myp71]

If I was going to use a 2N2222 buffer As Dale Y was saying.<p>What does the 2n2222 require You know when a power fet needs + trigger and input and output grounds is the 2n2222 the same or how does this work for the 2n2222

[dyarker]

Sorry, I'm going to have to leave you hanging. Still working 12-14 hrs a day 7 days a week. Too tired to analyze this.<p>But I think problem has to do with switch ground on and off.