Category Archives: Electronics Learning

Buying resistors

If you’re going to purchase resistors, don’t get these blue ones. The color bands that show the values don’t show up well enough against the blue background. They’re fine if you only use a single value, but if you regularly need to read different values they’re very difficult to read — at least for me, and I got a refund because they were so hard to read.

Get the ‘normal’ ones with a brown background

These used to be standard until, like too many things, manufacturers got cheap and started to use lesser quality.

And watch out for the ones that have extremely thin leads. All of the blue ones and some of the brown ones that I’ve purchased from China via eBay have had very thin leads that are difficult to handle and they bend way too easily which means they kind of crumple when you try to insert them into test boards.

I found resistors from a US supplier that have the brown background and the ‘normal’ fatter leads at a very good price. Here is their ebay store: http://stores.ebay.com/E-Projects-Electronics

Of course you can get them from other sources, too. I found them at www.newark.com and www.microcenter.com too.

All about the L298N H-bridge motor controller module

Oh boy, was I confused about this module at first! I found a fair amount of bits and pieces about it, but could not find the complete info that I was looking for. So I decided to create this tutorial for others who want to understand it better. I’m not an expert, but I have figured it out well enough to make what I think is a very clear and complete basic ‘primer’ on this device. Whether it’s right for your project is up to you to determine, but here’s info about the module itself, and especially about the mysterious jumpers (at least they were the biggest mystery to me).

What is it?

This module is a very inexpensive and convenient package based on the L298 dual full-bridge rectifier chip made by ST Microelectronics. It can be used to drive speed and direction for one servo or two standard DC motors, and drive other inductive loads like relays and solenoids. It can be controlled by microcontrollers like the Arduino.

Here is the description of the chip (not the module) from ST: The L298 is an integrated monolithic circuit in a 15-lead Multiwatt and PowerSO20 packages. It is a high voltage, high current dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors.

You can see the data sheet on their website here: http://www.st.com/en/motor-drivers/l298.html .

You could just purchase the chip and component parts and wire up your own parts, but this complete module is probably cheaper than the combined parts, and it’s certainly more convenient. As of January, 2017, the modules are selling on ebay for under $2.00! At this price they’re from China of course, but you can purchase them at higher prices in the United States if you can’t wait for the long shipping times from China.

I’ve read in forums that the L298 chip is about 15 or 20 years old, so there are better(?) chips available now. People seem to like the Pololu A4988 https://www.pololu.com/product/1182 .  Stepper motor current limiting is apparently one of the big improvements, but none of the current-limiting chips come in this neat module format that I’m aware of. So this L298N module is fun and handy, certainly great for testing and little projects, but be careful if you need current-limiting features when driving stepper motors.

How to use it

If you buy from the auctions on Ebay you get the typical Chinese-translated-to-English descriptions that are neither complete nor understandable. And searching for other resources on the internet or YouTube results in some great information, I was not able to find any one source that was all-inclusive like I’m hoping this one is (for a basic primer anyway).

So here’s how you use this little beauty to control the speed and direction of a simple dc motor.

You can use only this module and a power supply to control the motor direction and have it run at either full speed or stop completely. You need a micro controller like an Arduino if you want to control the speed of your motor anywhere between full speed and off. I’ll assume you are familiar with an Arduino. If not, you’ll need to learn that first.

Powering the module —

It runs on from 5 to 35V. That means you can run your motors, servos, or other objects anywhere in that range. Click the photo for a larger version.

The module itself needs 5V for its internal logic and can generate the 5V through its own regulator if you input from 7 to 12V. If you run your motors under 7V or over 12V, the internal regulator will not function and you will need to apply your own external 5V to the module.

There is a jumper that applies your input voltage to the internal 5V regulator on the module. You must not use that jumper if you input less than 7V or more than 12V. Less than 7V and the regulator can’t do its thing to create a regulated 5V. More than 12V and you will burn out the 5V regulator.

A red LED will light when the internal 5V is active.

 

So you use PWM (pulse width modulation) to control the speed of the motor, and two ‘enable’ pins to control the direction.

…More coming soon…

Using Arduino Nano and a relay to fire a solenoid

In my previous post I talked about using a motor, a cam, and a switch to fire a solenoid. That just wasn’t going to work because it was too hard to get the right pace of the solenoid firing. The motor voltage changed its speed, and the cam idea was too difficult to adjust the cam shape and location.

In this post I’m showing how I switched to the Arduino Nano to control the firing rate of the solenoid. With the Arduino, it’s a 30-second program change to change the rate of the solenoid firing as opposed to the ridiculously difficult process with motor and cams.

The first video below shows the solenoid firing using the default settings in the sample ‘Blink’ program in the Arduino IDE.

 

The video below shows the solenoid firing after I modified the delay settings in the ‘Blink’ program.

Series Circuit Defined

A series circuit is one in which items are arranged in a chain, one following the other, so the current has only one path to take. The current is the same through each item.

Series circuits are used for several reasons:

1. To increase a voltage source.

The following is true of any standard battery, but let’s use the AA battery as an example. If you put one AA battery in a circuit, you will have a power source of 1.5 volts because that’s the voltage of a standard AA battery.

AA-battery

 

If you want 3 volts, you can place two AA batteries in series which gives you 1.5 V + 1.5V, which equals 3V.

AA double batteries and lamp

 

 

 

 

Put three AA batteries in series and you will get 4.5 volts, etc.

More coming soon.

 

Also see: http://physics.bu.edu/py106/notes/Circuits.html

Your First Electronic Circuit!

So you want to learn about electronics! Good for you! The sky is the limit when it comes to this field, but let’s start with a very simple circuit.

Lighting up a light emitting diode (LED).

The entire circuit is very simple — it consists of an LED, a power source (batteries), and a resistor to limit the current through the LED.

Light emitting diodes will emit light when a voltage is applied to them and current flows through them. Different colors and types of LEDs may require different voltages and currents, but a standard red LED requires 1.7 volts and .02 amps (20 milliamps, or 20 mA).

Here is a how to build your circuit if you’re a very beginner without many tools yet.

basic LED circuit

I have two AA batteries (1.5 volts each) that are connected in series to make about 3 volts. (Click here to learn about series connections.)

They are in a little battery holder with alligator clips that I soldered on to make the connections easier.connected to the LED and a current-limiting resistor.

I used an extra alligator clip to connect the resistor to the LED. You could use a paper clip, or just wind them together.

Here is what the circuit looks like in a schematic diagram:

basic_circuit_schematic

Even this simple circuit needs a little forethought.