Why does the battery voltage change?

Today I got a question from Garry on the Ohmify community.

[GARRY]:
“When I measure the voltage of my 9V battery using my multimeter I get a reading of 9.06 when it is not connected to any circuit. When I hook the battery up to a simple circuit (i.e. 325 Ohm resistor in series with a red LED) and measure the voltage drop across the battery I get a reading of 8.65 V – why the difference?”

What happens when you force 3V onto a 2V LED?

I remember something I struggled with in the beginning.

The LED.

It’s supposed to have a fixed voltage drop, right?

Like 2V.

But what if I force 3V across its legs with a 3V battery?

Resistor before or after LED?

I just published a new video where I answer the question:

“Does the resistor go before or after the LED?”

If you don’t want to watch the video, I’ve attached the script below so you can read it instead:

The resistors-in-parallel mindtools

Imagine a circuit with two resistors in parallel.

If you’re not sure what that looks like, look at this image:

Let’s ignore the values above and instead say that R1 is 100 Ω and R2 is 100 000 Ω.

Can you quickly find the combined value of the two of them?

What if both of the values are 300 Ω?

You *could* use the formula for resistors in parallel and calculate it.

But there’s a quicker way.

How to build a cool touch-sensitive lamp

Build a circuitHere’s a fun project.

Build a cool touch-sensitive lamp you can have on your desk.

Once you’ve built this project you can also apply the touch control to other things like a fan or a door bell.

The first thing you need to figure out is how to sense touch from a finger.

Mathematics for Electronics – What Do You Need?

pcbI like math.

But, I’m not an expert.

I know the basics.

But when it comes to more complicated stuff, like heavy derivation and integration, I think I’ve forgotten most of what I learned at the University.

How to use analog sensors on Arduino

8x8x8_arduino_10These sensors are usually cheap.

And really easy to use!

An analog sensor is a sensor that gives you a voltage value that represents the measured value.

How to transfer a C program to a chip?

chipPer wrote me:

“What’s the easiest (cheapest) way to transfer a C program to a chip?”

Here’s my reply:

It depends on what chip it is.

Most microcontrollers require a programmer. This is a little thing you plug into the USB port that makes it possible to program the chip.

How to fix your blinking relay circuit

Blinking an LED using a relayI really like the circuit that blinks a light with a relay.

Like this:

If you connect a battery to the electromagnet of a relay, through its normally closed contact, you will get a relay that switches on and off really fast.

If you add a big capacitor (like 1000 µF) over the electromagnet, the electromagnet will stay on longer.

Mythbuster: Can you fix broken computer parts in the oven?

usb-mouse-kretskort-underI’ve done some research.

A couple of weeks ago Tek.no, a Norwegian tech-magazine, asked me if I could write an article for them.

There are a lot of people online claiming they have fixed broken graphic cards and other hardware, by baking it in an oven.

10 things you can build with electronics

protostack-board“What can you build with electronics?”, she asked me…

“Anything!” I said.

She looked at me with a blank stare. Apparently that was not a satisfying reply.

This happened to me a few days ago.

Sometimes I get too deep into electronics that I forget “normal” people don’t necessarily understand what you can do with electronics.

So…