E1: Driving LED’s without resistors

This is part 1 of a 4 part series on the design and creation of a digital dice that can be used to teach children about electronics and/or programming. The design and training material will be available for free once it’s done.

While I was working on this “project”, I questioned everything and I found myself some unexpected answers. Let’s start with these questions and their answers. It allows you to determine whether or not you are interested in this series at all.

  1. Do we always have to use resistors when we use LED’s in battery powered devices?
    Answer: No.
  2. Is it difficult to program your Atmel chips without anything Arduino?
    Answer: No.
  3. Can we reduce the standby power consumption of an ATTiny by so much, that it’s cheaper to not add a power button and keep it on standby forever?
    Answer: Yes.
  4. Can I use basic components to create a device, that allows me to measure current draw in nano amps very easily?
    Answer: Yes.

I will use these questions as the guideline for this series. In every post I will try to cover one question and provide you with a more detailed answer.

This week it’s about driving LED’s without resistors.

Context

The device has to be cheap and not contain components that we do not need. If we can do without resistors, I can cut on both the costs and the complexity. Now can we?

Answer

Yes we definitely can, as long as we select the right LED. The device is powered by a CR2032 3V battery. Thus, if we select a type of LED which has a Forward Voltages (Vf) above 3V, we should be safe.

When we look at the following graph from www.electronics-tutorials.ws we can easily see that a green coloured LED would fit our project perfectly.
I/V Characteristics Curves showing the different colours available

The data sheet for the ultra bright green LED that I had lying around and current measurements I did, supported the graph. I never measured more than around 13 mA of current flowing at 3V.

The ATTiny that I had in mind to control the dice can drive 40mA per output pin and a total of 200mA, so we can run 6 LED’s perfectly fine within the specs and without resistors!

That’s it for this week. Next week I’ll cover programming an Atmel chip without Arduino which is a lot easier than I thought.

Blockchain is bad for the environment

How can a technology be bad for the environment you might ask. Well, here’s why.

Blockchain is as safe as it is, because its security is based on raw computing power. Right now there are thousands of computers around the world that are executing complex calculations to ensure validity of transactions worth a few pennies. Ever thought of that? The people or companies that are making money on blockchain technology are actually trading energy and not in an effective environmental friendly way.

Why do we hype stupid technology?

The Raspberry PI is not a $ 35 computer

I am a real big fan of the Raspberry PI foundation. They do make some awesome devices that indeed enable a lot of people around the world learning robotics, domotica and programming. Hell this blog is hosted on a Raspberry PI 3 and it works like a charm. So I am a real big fan, but there’s just one thing that continues to annoy me. The prices that everybody mention when they are talking about Raspberry PI’s. The PI Zero is being called the $ 5 computer and the PI 3 is being called the $ 35 computer and these prices are simply not correct.

The real price

If you want to use the PI Zero you do need at least an SD card. Depending on the type and size it will cost you an extra $ 10. But you also need a power supply, which will add another $ 5 to the bill and then, well if you want to attach a keyboard, mouse, WiFi or Bluetooth, you will need a USB adapter and USB hub which will add at least another $ 5 to your bill. And then you might want to protect your PI Zero, so you’ll need a case that costs at least $ 5. So you will end up with a bill of $ 30 which is 6 times as expensive as the mentioned $ 5. Truth to be told, you can reuse the USB adapter and USB hub on another PI Zero as long as you do not require any WiFi or Bluetooth connection at all or buy a PI Zero W which costs $ 10. So $ 30 is really the bare minimum price you can get a away with.

If you want to use the PI 3 you’ll need to add an SD card, a decent power supply – I highly recommend you to use the official Raspberry PI one – , and case and you will end up with a total of at least $ 40 + $ 10 + $10 = $ 60.

Conclusion

If you want to use a Raspberry PI in any of your projects, by all means do. They are really great machines and very good value for money, but don’t expect you can get away with spending just $ 5 or $ 35 as they do cost you a lot more.