Tweet
Universal vibration-circuit for all metal-detectors!
Enjoy! 
-
-
I've re-drawn the circuit in a way that everyone can understand.
It seems you are using the op-amp as a comparator, shorting the output to ground causes a high current draw from the battery, and hence through the vibe-motor.
I suspect the operation of this circuit will depend on exactly which LM358 you use - which manufacturer, which batch, etc.
Many machines will output a high voltage level if you don't put a load on their audio output. They may be 10 Volts, no load. They fit a series resistor, typically 330 Ohms, in series with the headphone output. It's assumed that headphones will be 50 - 200 Ohms, so this will drop the voltage down to a more modest 3 V or less. I think your circuit should have a 'dummy load' on the input, something like 100 - 220 Ohms would be a reasonable value. -
Thx for your interest.
And its good to have somebody here which sees it from a different angle
for potentially further improvements (if possible at all... ).
An op-amp comparator circuit would be like this here and
it's possible with such a 2in1 amp IC like the LM358 to create it:
http://media.wiley.com/Lux/43/309543.image3.jpg
taken from here:
How to Use an Op Amp as a Voltage Comparator
http://www.dummies.com/how-to/conten...mp-as-a-v.html
Of course eiter the op-amps technical specifications (its amplification rate etc.) must not change
or otherwise the circuit adjusting resistors need to be a bit higher or lower.
But I doubt the tech-specs will chance alot. At least not if always some LM358N is used
and no LM158, LM258 etc.
> Many machines will output a high voltage level if you don't put a load on their audio output.
> They may be 10 Volts, no load.
Sorry but that's wrong with MDs output.
Simply take some voltmeter and a diode and measure it.
I did it and the flowing voltage is extremly low, around 0,01 -0,05v for weaker or half-loud audio-signals.
And my opinion is that its no option to use some permanent dummy load for the input
because it would reduce the sensitivity enourmous!
Per instance you can't change the 470k resistor to lower otherwise the
amplification already no longer works very good or at all.
That high impedance input works already with very low AC-signals
and its possible to adjust it with the variable restistor.
The only method would be to amplify first the audio-in AC signals 10x
if you want a dummy load because the audio out of some MDs is really quiet,
especially the also important and short snap, crackle and pop signals.
Another important factor is that those motors don't react immediatly.
They have some lag. To make it professional the vibration-signal should be modulated.
Here some article about such special vibration patterns but of course an additional
programmable IC is needed to get such special vibrations
(for example 2 -4 -6 vibs per second, weak vs strong turns etc.)
http://www.precisionmicrodrives.com/...ting-waveforms
The ohms of the headphones means only how loud they are or how much power input they can take.
A 32ohm speaker is much louder with 100mV input as an 8ohm speaker,
but the 32ohm speaker will start to distort or blow and make bad signals if a volume (AC-audio-voltage) is applied
which is heavier than some perhaps too small speaker can bear.
Of course the power of the output of MDs is not that strong as HiFi-line-out, its even pretty quiet.
Probably its never more than 0,4v and the little signals are 0,05v.
btw. usually the lowest audio-out comes from a mic or un-amplified vinyl-records player needle.
Anyway: The audio-ohms-output not counts because the vibration circuits input works with
super high impedance and every voltage from 0,001v to 2v will be extremly reduced totally.
This is not a direct wire that goes directly connected over some earphone-coil with neodymium magnet.Comment
-
Vibration-circuit for metal-detectors schematic [super high sensitivity version!]
Comment
-
Of course formerly resistor #5 in the high sens version must have #4 now cause
the earlier #4 resistor was removed. This was corrected in the below schematic.
btw. the usual "quiet" value for the var R3 and R4 in the normal version and
for the var R3 in the high sens. version is 62k Ohms (a 47k plus 15k resistor).
For devices with louder audio-output like smart-phones or laptops!
Values lower than 62k like just 47k make the whole circuit unsensitive, but:
For pretty quiet MDs or weak audio-devices up to 470k should be used or even
the switch that cuts off the connection between non inverted + input and gnd.
In most cases with the variable resistor the exact sensitivity point is adjustable.
A good test possibility is to connect some mp3-player, set the volume to half,
play the song (it should vibrate) and press pause (now the vibration must stop).
The quieter the song is playable (use a rock-song where always is enough power and not
some classical or esoteric instrumental stuff) while it still vibrates the better but of course
pressing pause while everything else remains connected always should stop the vibrations.
Comment
-
Comment