Rookie tips

[petey twofinger]

http://www.beavisaudio.com/techpages/Transistor-Pinouts/index.htm

http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/The-Mod-Zone-_/TRANSISTOR_SUBSTITUTION_CHART.gif.html

[gcme93]

There is a quick check for breadboards drawing too much current - before applying power, measure the resistance between power (+9V) and ground. If you have say 100 ohms resistance, then the current will be at least V=IR, 9=I x 100, I= 90mA. Most chips draw a few mA each, bias resistors much less, its a good guess that most analogue circuits will draw less than say 30mA. So if you measure less than 300 ohms, then double check your circuit. Most circuits I have built measure well over 1K from power to ground. After I cooked a battery, I always do this check.

Stolen straight from Ronan but quoted appropriately. Seems like a sensible thing to do with any build before you attach your power.

[Kipper4]

how do i measure what amperage a circuit is drawing?
Its time i learnt this. I'm sure my DMM is capable of it, I've just never done it or been aware of the need.
Thanks for any help and advice you can give

[davent]

I put together a small box that puts a 1Ω resistor in seies with the battery +ve.  Battery/power supply plugs in one side the pedal plugs in the other side. Set the DMM to read mV and measure the voltage drop across the 1Ω resistor and that converts directly to a mA reading (ohms law).




As a matter of course i put a 100Ω resistor between the battery and the circuit with a 100µF cap to ground so if the pedal is only battery powered i can always measure the voltage drop across that resistor and calculate the current draw from that into.
dave

[Kipper4]

That just went right over my head i'm affraid.
Sorry for the dumb question but what does the  Mv    setting look like on the DMM
Is it the 200m/2000m setting in the DC voltage range?

DMM Pdf below if this helps.
http://www.drapertools.com/products/manuals/60792ins.pdf

thanks
i wish this was a video on you tube with explanations.
Thanks for all the help.

[davent]

It wil be the lowest DC volt setting on your meter, measures milliVolts. Still waiting for the pdf to open but on all mine the lowest setting is 200mV.
dave

[davent]

Can't do a video but this shows the setup.



Meter is set to read up to 200milliVolts (mV) so by ohms law, Current(mA)= Volt(mV)/Resistance(ohms) and since the resistance is 1Ω the meter can be read as mA even though the meter is set to the volt scale.
dave

[Kipper4]

thats making more sense now i can see how the meter is hooked up thanks.
I'll give this a go soon and start learning ohms law and its applications soon
thanks Dave

[duck_arse]

or you could use the dc mA range. stick the meter in series with the power supply and the circuit.