very basic help required please.

[aljaxon]

hi i have a basic grasp of electronics (or thought i had!!) and then i decided to have a go at building this simple circuit to turn 12vdc from a motorbike battery into voltage that could be fed into a mic socket and recorded.
View attachment 66719

i want to know 3 things please. forgive my ignorance.

1/what is R2 doing? apart from almost short circuiting the battery.
to me R1 and R2 are short circuiting the battery. but i realis a bulb in effect is short circuiting the battery but gives out light and is using energy or current? which stops everything from frying.

2 i know how diodes work in theory. but what is the point of the 2 diodes D1 and D2?

3/ what is R4 doing? why isnt it just next to R3 and the vertical line that passes through R3 on the diagram rubbed out/erased/left open for want of a lack of vocabulary.


so basically why arent all the resistors placed in a line to give the required resistance?

thanks for any replies and many apologies for my ignorance.
i am trying to learn and have searhced for stuff and read loads and been told what happens but not why.
so frustrating!!!
i mean i have built this thing and it produces 1.5mV but i want to know why then i dcan start to create my own. as i need one to output 15mV or higher. or at least something that will register on a mic input of a camcorder or laptop.
then what i do with it is another question altogether but one step at a time.
cheers!!!

 

[ericgibbs]

i want to know 3 things please. forgive my ignorance.

1/what is R2 doing? apart from almost short circuiting the battery.
to me R1 and R2 are short circuiting the battery. but i realis a bulb in effect is short circuiting the battery but gives out light and is using energy or current? which stops everything from frying.

2 i know how diodes work in theory. but what is the point of the 2 diodes D1 and D2?

3/ what is R4 doing? why isnt it just next to R3 and the vertical line that passes through R3 on the diagram rubbed out/erased/left open for want of a lack of vocabulary.


so basically why arent all the resistors placed in a line to give the required resistance?

Hi,
The designer uses R1 and R2 as a voltage divider for the 12V input.

The divided voltage out is ~0.53V, this voltage is further divided by R3 and R4 to give 1.7mV at the output.

The purpose of the two diodes would be to clamp the voltage output of the R1/R2 divider to approx +0.6V in the situation where the input was greater than 12V. The second diode would clamp at -0.6V in the situation where the input 12V was accidentally reversed.

The diodes would limit the output voltage in order to protect whatever the output is connected too.

Replacing the 33R with a 270R would give the required +15mV output.

 

[alec_t]

something that will register on a mic input of a camcorder or laptop.

Why are you trying to record the 12VDC motorbike voltage? Most mic inputs expect an AC signal, not DC, and probably have a DC-blocking capacitor at the input.

 

[JimB]

Aljaxon wrote:

i decided to have a go at building this simple circuit to turn 12vdc from a motorbike battery into voltage that could be fed into a mic socket and recorded.

I have to ask, why would you do that?
You cannot play it back later and re-charge the battery

An audio recorder will not record DC, it will only record AC at frequencies between 20 hz and 20 khz.

JimB

 

[aljaxon]

well thanks for the replys but the language used in the first explanation is assuming i have a certain level of understanding which i dont. i almost get it...

basically i need to convert my bikes voltage into something a mic socket of a camcorder/ laptop can record and feed the resultant wav file into some software that will understand and decipher what rpm i am doing.


i am analysing my bikes alternator ie rpm using some software by feeding it .wav files of the engine under load. like a diy dyno that feeds off and analyses sound files.
i have been inputting simple microphone recorded actual sound files but it can be much more accurate if fed the actual voltage but reduced to a level a mic can record.
.i am told i can connect the "divider " to my battery and it will still create a signal with enough information that the software can process and turn into rpm.

the webpage is here

http://atom007.heimat.eu/tmt/gsf_dyno.html#Dynamo

cheers for trying to help me.

 

[aljaxon]

edited

 

[audioguru]

Your new posts will be moderated until you have posted about 10 posts to make sure you are not a Spammer or worse.

 

[ericgibbs]

hi aljaxon,

There are no posts in the Moderation queue.???

Moderation.

Double checked on this Thread.
All your 3 posts of today are visible.

Posts #1, 5 & 6

 

[aljaxon]

i just posted it then noticed a mis-spelling and tried to edit it but it wouldnt let me and i noticed the moderation tag. and it stayed like that despite refreshing for half an hour.
its ok now.
thanks to ericgibbs ive changed the 33R to a 270R and am about to see if my laptop detects it via the mic input.

i have spent hours today trying to learn the basics of electronics and need something that is a buit more dumbed down than erics explanation.
thanks

 

[audioguru]

There must be a rectifier arrangement between the alternator and the battery to convert the AC from the alternator into DC to charge the battery. In a car the alternator has a pulsing DC output because the rectifier arrangement is built-in. The battery smoothes the pulses.

You need to record the AC output from your alternator ahead of the rectifiers, not the 12VDC at the battery.
The signal from the alternator will probably be a much higher frequency than the engine speed.

 

[KeepItSimpleStupid]

The big problem is that D1 and D2 limit the maximum voltage to approximately +-0.6V. That is a typical circuit for a clamp.

The first voltage divider does two things:
1) Divides by 2; If this is 12 V, then it divides the voltage to 6. (Nope - See Eric's post below)
2) It limits the current through the diodes.

Then it's followed by another voltage divider.

 

[ericgibbs]

hi Kiss,
R1 and R2 are the first divider 10K and 470R respectively, which is approx 0.53V at the junction.

E.

 

[KeepItSimpleStupid]

Again thanks. Eyes. Thought it was 10K, 10K.

 

[aljaxon]

well, with my new upgraded divider i manager to record the voltage at the battery terminals and as the engine revs rise you can hear the voltage signal recorded rise and fall just like the sound of the engine.
so it works!!!
but the software i am using refuses to accept the .wav files that the laptop produces. even if i try converting them using other software to mp3s and then back again.
i got the same error using my camcorder but found if i extracted the audio using a certain program the wavs were accepted.
the error wont mean much to anyone on here "index exceeds matrix dimensions"
so instead of a laptop i am gonna try a phone to input the mic/divider.
i darent use my camcorder for 500 obvious reasons . . .

its a shame because i know how to get the output voltage from my divider by changing the resistor but i still dont know why it works

can anyone explain post 2 but in laymans terms? the clamping bit i dont understand how it is doing that?
thanks

 

[ericgibbs]

ts a shame because i know how to get the output voltage from my divider by changing the resistor but i still dont know why it works

can anyone explain post 2 but in laymans terms? the clamping bit i dont understand how it is doing that?

Generally diodes only conduct current in one direction when a DC voltage greater than the diode turn on voltage is applied.
The diode turn on voltage is around 0.6V to 1V depending upon the diode type

so:
The triangle of the diode symbol is the Anode and the Bar is the Cathode.
If the voltage applied between the Anode [+v] and the Cathode [-] is less than 0.6V, the diode will not conduct current, when its greater than 0.6V the diode will start conducting.

If we now reverse the voltage applied to the diode, so that Anode[-v] and Cathode is [+v] the diode will not conduct.

You will see on your diagram two diodes are in reverse parallel connection.. the anode of one diode is connected to the cathode of the other diode.

So now if a voltage less than 0.6V is applied across the diodes , neither will conduct.

If the applied voltage is say +1V, the forward biassed diode will conduct and clamp at +0.6V,,, if now the applied voltage is reversed -1V the other diode will conduct and clamp the voltage at -0.6V.

The resistors of the first divider will limit the current flowing thru the diodes

This clamp diode circuit will therefore never allow the voltage to exceed +/-0.6V across the diodes.

This clamped voltage is applied to the output resistive divider.

Do you follow OK.?

 

[ericgibbs]

hi,
Look at this plot.

The top plot shows the battery +V wire changing from -15V thru to +15V.

The middle plot shows the effect of the diode clamp approx +/-0.6V

The bottom plot shows the Vout, never exceeds +/-15mV

OK.?

 

[alec_t]

"index exceeds matrix dimensions"

but the software i am using refuses to accept the .wav files that the laptop produces

Perhaps extract a short section of the wav file (using an audio editor such as Audacity)?

 

[aljaxon]

why does the voltage go negative? and necessitate a diode going from the negative to the positive wire? this is my sticking point. also to reduce the voltage why not just have two resistors in series that reduce the voltage down to the required level?

and the gsf dyno program doesnt like anything that has been processed by either adobe premier or soundbooth. no matter what i do it wont accept them. i have to use windows movie maker and then switch sound converter. if i use switch sound converter after adobe programs it wont accept them.
strange. and now it seems it doesnt like windows sound recorder. the gsf dyno can cut and trim the wav files.

 

[ericgibbs]

why does the voltage go negative? and necessitate a diode going from the negative to the positive wire? this is my sticking point. also to reduce the voltage why not just have two resistors in series that reduce the voltage down to the required level?

You will discover that on vehicle ignition system you can have high voltage spikes, both positive and negative, this is in fact how your circuit works, it detects repetition rate of the spikes due to the ignition/magneto system which are proportional to the engine rpm.

The diodes are there to limit these spikes to around +/-0.6V, without the diodes the output to your recorder could exceed the safe input limit for the recorder.

 

[aljaxon]

thanks eric, i know mine is a 12 volt system but can produce spikes as high as 50V. i am downwind of the rectifier so i should just be getting positive dc volts?

i dont know what the safe limit of my camcorder mic input is.
my phone mic input doesnt disable the phones on board mic so i am getting the sound recorded as well!!!