Hey Guys. SO i;m new to the forum and signed up to ask this.

I have a project where i'm modifying one of these

http://www.homedepot.com/p/BLACK-DECKER-Auto-Tape-Measure-ATM100/100081220#.UiSKfjZHIjs

I Basically want to be able to plug it into a wall charger (get rid of the batteries 4x AAA) and be able to have some kind of timer so i can adjust how long the tape reels out for ( i hope you know what i mean). It currently has a rocker switch on it so in and out function where you have to hold it down.
ideally i would like to be able to set the time the motor expels the tape (unitl it reaches 2metres) then the timer ticks over, motor stops and the tape stays out there.. What do you think? im a rookie, studying mech eng but it has done me no justic with for the practical side of electronics.

cheers

 

I did one of these a few months ago. It's a simple motor with a rubber wheel that cranks the tape out, and a coiled spring does the rewinding just because you pressed a button that moves the drive wheel away from the tape. This can be done with a 555 timer configured as a "one-shot" and you dial in the time with a potentiometer.

It will not rewind the tape, and the tape measure will be useless for any other job because you will have to take it apart to get the pushbutton switch out of the way of your power supply.

If you still want to make a 2 meter tape ejector, look up, "one-shot" or, "monostable" on this site.

http://www.allaboutcircuits.com/vol_6/chpt_8/4.html

 

So once i get my Black and Decker tape, ill pull it apart and find a spring coil + a rubber wheel attached to a motor.

Before we skip to the timer, how do i convert its power-source from batteries to plugin. I don't need it be portable, SO i need a AC - DC power adapter, im guessing something like a 6 volt output? Snip the ends, get my voltmeter out and figure where the power is coming from then hook it up to the battery pack minus the batteries?

 

Yes. Try to find a Wall Wart that does 6 volts DC, but first, measure the amps that the AAA batteries are providing while the motor is running.

 

Okay so once i have acquired my wal wart and connect it. is this the kind of setup I'm looking at
http://www.youtube.com/watch?v=zmUO9xLceEs

If so how do i incorporate a potentiometer? #12 do you have schematics or photos you could post??

 

You look at the page I sent you to in post #2 and modify that circuit to be adjustable and start with a push button. This circuit MIGHT work because it can deliver 2/10 of an amp, but you have not told anybody how much current the motor needs.

 

Like i said i'm a rookie. appreciate your help. I should get the tape soon so will test it for amps and go from there. need to buy a bread board as-well by the looks of things.! #12 thanks again.

**quick question

Since T=1.1*Rt*Ct

can someone explain what the Rt and Ct values are?

something to do with the relationship between the capacitors and resistors?

 

This calculator might help you.

http://www.bowdenshobbycircuits.info/555.htm

Here is the Monostable page showing a 3 sec duration.

http://forum.allaboutcircuits.com/showthread.php?t=14018

 

The Rt and Ct values are on the schematic I made for you. 10uf and 220k + a variable 100k resistor.

 

#12 so in order to change the interval i would need to change the value of my resistors and caps?

 

That or use a potentiometer, which is a variable resistor.

 

#12 so in order to change the interval i would need to change the value of my resistors and caps?

Yes. That is their only job...to set the time interval. I included a variable resistor because I know that the tape measure I worked on a few months ago took about 3 seconds to eject 2 yards of tape. On the other hand, I was fixing it because it was old and corroded. A new tape measure might be faster. That is why I included a variable resistor, just turn the knob.

 

Ok, this is where i'm at.








Now #12 you are right. about everything, i just don't understand how to use the 555, so a variable resistor is like a Phillips head thing that i can turn up and down to adjust the timing interval [or a knob]

So i have only ever used a breadboard once before so really have no idea what im doing. but i will give it a shot!

 

slowly but surely getting there!

Okay so one more question! should the output after it goes through the motor be grounded instead of going to the positive side?




And what does B represent?

 

1) No.
2) "B" represents a point you are not using for a start command.

and, still, you have not told how much current the motor needs, so I can not be sure you don't need a high current transistor to help the chip.

 

Okay #12 i got this far. Went out today and bought what i needed (well what i thought i needed).

what i bought was.

ZL3555- NE 555 Timer
Bread Board
RR0628-Resistor .5W MTL 220K (x10)
RR0596-Resistor .5W MTL 10K (x10)
RR0620-Resistor .5W MTL 100K (x10)
RP3518-POT PCB LIN SG 24mm B100K STD IMP SHAFT
SPO700-Switch Push MOM SPST N/O
RG5125-Capacitor GRN 100N 100V P=7mm (x2)
RC5360-Capacitor CER NPO 100N 50V 10% p=5mm PK2











So i put it all together, and all i get is a really warm IC... Please help me in what im doing wrong. (obviously the batteries are in there. )




Just realizing that my pictures aren't really the best.

 

Could you move that one red arrow a bit? It's covering the 2,6 & 7 connections. You've probably got those right but we can't tell for sure.

That snubber diode is needed to dissipate the energy in the motor windings when it is turned off. Without the diode, the energy has to go somewhere and it usually finds an IC to ruin. It's not optional!

[update] Nevermind the first question, I see you posted earlier versions of your schematic. The main and obvious question is the one #12 raised that you haven't answered - power draw of the motor. It may be more than the IC can handle, so the motor doesn't move and the IC gets hot.

 

Okay, so i need a snubber diode and im guessing that will depend on what the power draw of the motor will be?

i have been trying to measures the amps but my Ampmeter either A) isn't reading it correctly or B) im doing it wrong.

IF it helps the original switches i pulled out of it were rated at 3A125/250V

 

Yes, I think the rule-of-thumb is that the diode should be rated to at least double the motor's running current, or maybe even the stall current. There's no reason to skimp.

The switch ratings really don't tell much since they might be absurdly overrated.

Your ammeter needs to be in serial with the load, with the leads attached to the right ports of the meter and the meter set to the proper scale. The position in the series loop doesn't matter but polarity does; red leads go towards power supply positive. Start with the larger (10A?) scale first and see what you get. Use the smaller scale (200mA?) only if the initial reading is in that range.

 

okay so with this setup



It read from 3.123-3.268 Amps, and the motor would just be turning over (like 2 rpm) or stopped

So what kind of diode will i need for this one? Also do need to get a NEW 555 timer? or will it be okay?