Embedded Systems Programming Course

So a week or so ago i was talking with a friend of mine, Simon about how he was wanting to get into embedded programming and what that would entail. He had come across a series of youtube videos that take the unenlightened of us and walk us through many examples of becoming proficient with toolchains that allow for programming ARM micro controllers.

Now, I can do quite a bit of superficial programming in C using the arduino, but it does hold your hand quite a lot and its great for simple things, but if you want to do anything serious you really have to man up and learn how to use IAR Workbench or some GNU C toolchain along with all the associated hassles that come with that.

For sometime I have been using STM32 and ESP8266 micros but wimping out and using arduino for programming those chips, but after seeing this course on how to do ARM programming using the right tools, I have decided that its time to give it a go and see if I can get my head around the whole idea. So i ordered the TI development board from Element 14 and it arrived today so now there are no excuses. Time to start learning ARM programming and perhaps soon i might be able to turn those new found skills into a DSP IF board for homebrewers. No promises, failure is always an option 🙂

And here is the link to the course ware for those who might be interested in all this as well and want to give it a crack. http://www.state-machine.com/quickstart/


TDA2822 Audio Amp

So I have had this pile of Ebay sitting on my desk for sometime and today I have gotten excited enough to actually start taking a look at it all and seeing how it works. I got these frequency generator chips for like a buck and after setting them up with the test circuit, i could not get them to work, it happens, now and again you get Ebay’d in the butt.

So I figured next i should test out the TDA2822 audio amps. I for 50 for 2 bucks which is a lifetimes supply. Do they work, well, yes they do and here are the results.

Here is the test circuit straight out of the PDF. As you can see parts count is low. So I put the IC on the breadboard and used just 1 1/2 for a mono amp. I also used just 2 caps, pin8 to ground, 470uf as it was already on the breadboard and the input cap on pin 1. Powered with 8v as its a handy voltage i have on my breadboard. 12v would probably be a better option to allow for a larger voltage swing.

As you can see, nothing fancy here, just the IC and 2 caps and my signal gen and oscilloscope probes doing there thing allowing the pixies to in and out and display them in the screen.

So we stick in 0.1v 600hz sinewave and see what happens.

Well, we actually hit the voltage rails and clip somewhat. 0.1v in almost 8v out, that is the voltage gain there. And when i do some da finger poken, the IC itself is cool to the touch, not warm, not hot, but about the same as ambient temperature of the room. So i am thinking Bye Bye LM386, and hello life time supply of TDA2822. And being a stereo IC, I can also bridge the left and right for even greater output. Not that I think i would need it.


8Mhz Signal From Arduino

So you might be thinking, Bullshit, you cannot get an 8mhz pwm signal out of an arduino. But you can. Ignoring the sine like shape of the waveform below for a minute, that is the actual PWM output from an arduino uno I was using to do this. So, why is it so.

Well, all you have to do is use some code wizardry using interrupts, timers and registers in such a way that the maximum pwm frequency you can get from most microcontrollers is 50% of the clock speed. Given that the arduino usually has a clock speed of 16mhz, this gives an actual maximum pwm out of 8mhz. And while this is nice, in practice it is not all that useful as the discrete numbers of frequencies that can be derived this way is not all that useful.

The code is below, I did not write this code and sorry to whomever did, I do not have a link back to it and your name was not included in the snippet, so i cannot credit you. Enjoy.





Arduino Memory Keyer

Ok, so it looks like a mess on the breadboard, and you would be right, its a bloody mess and there is so much other left over other projects that it is almost impossible to tell where the crap ends and the keyer begins, but i can assure you, its there and it works. I used the morse library written by Erik Linder SM0RVV and Mark VandeWettering K6HX and fixed by Glen Popiel which can be gotten from his website here: With a minor change to the header file in the library to make 2 private methods public, we are now able to individually key dits and dahs at the correct speed without delay overheads.

Connecting the key to the arduino is as simple as using 2 10K resistors in series to 5v to pull things high. And when you key a dit or dah things get pulled low, we read that change on pins 10 and 11 and send the dit and dah accordingly. Very much how PA3CHM did it here: in his simple keyer.

And because the morse library takes care of timing and can send strings of morse characters, it was a rather prospect to add in a 4 button keypad, fiddle with the example code in arduino and get some memory functions happening. So i have 2 hard coded memory calls, which call cq for me. This could be expanded with a larger keypad but suits my needs. The other 2 buttons are used to set the cw keyer speed, incrementing or decrementing the speed 1 wpm at a time.

Now obviously there are some rather full blown arduino keyers out there that have all the bells and whistles you can imagine, and yes i could have used the code by K3NG here: but i chose to roll my own specifically to my own needs and ultimately this will embedded in the 3 band cw rig i have been working on for sometime. The good thing is I have this part working, its timing is fine and now I can move onto the transmitter part of the project.

The code is published below, I hope others find it useful, take it, modify, expand and customise to your own needs. Enjoy.




So You Want To Make A Sine Wave In Arduino

So a bunch of blog posts back I posted how easy it was to get a square wave out of an arduino to do things with like generate your 600hz tone for CW etc. But we can go 1 further than that and use the arduino to generate sine waves. Of course you can filter the crap out of a 600hz square wave and make a sine, but to be honest, who really wants to wind inductors in the mH range or for that matter build a suitable LC filter to cut out the harmonics sufficiently to make a sine wave. But alas poor Yorick, there is a way and its called PWM.


So above we have a 31khz pwm signal that is being used to generate a sine wave. Through the wonders of mathematics and other nerd endeavours that PWM signal can be used to make sine waves, in my case a 600hz sine wave. Now obviously you still need to filter off the crap to see the sine wave, but its there and below is the filtered output. Now the good thing is you can filter with RC filters and make life simple. In my case i am using a 2 pole RC filter using 100nf caps and 2K resistors, and as you can see it looks rather sinusoidal.

So the following software is not mine, its something i found on the net and did some simple modifications to make work with an arduino UNO. Output is from PIN 11. Take a read, you should be able to work out how it works, using interrupts and timers to get some semblance of accuracy. Anyway, enjoy and have fun.

So I have cleaned up the original code to make it easier to read and to remove the stuff in there that was really doing nothing. And here is a link back to the original article. http://interface.khm.de/index.php/lab/interfaces-advanced/arduino-dds-sinewave-generator/


Wemos WiFi and Fun With Clocks

I’m Dr Sheldon Cooper and welcome to another exciting episode of Fun With Flags. We, humor aside, trying to get an accurate time on a micro can be done a multitude of ways and I have given them all a crack this time around and will use 2 out of 3 in my latest project.

So being WiFi enabled, i can call the time of an NTP time server, get the Unix time, do some math wizardry to make the time usable and bing bang boom you have the time. Trouble is, i was getting a number of failed packets and this is of course bad and was making my time keeping go off. Even if i was detecting fail packets and polling again for a new packet, it could wreck my other data and put things off. So, it had to go.

Of course you can call the millis function and do your own time, and I do this for some of the other non critical timing functions, like do this every 5 minutes or do this every 10 minutes, where if the clock drifts by a few seconds its not all that critical. I did make a functioning clock this way and I was getting about 2 seconds drift per day, easy enough to correct for but the code was ugly and you had to reset the time and date everytime i rebooted, and for testing it was a pain in the arse.

So i busted out a real time clock and connected her up and of course this is always going to be a superior option and the one i should have went straight for rather than stuffing about for a couple of nights giving each of the other guys a crack. Oh well, I learned a whole lot in the process and now she is a choocker. Oh and BTW, there are a number of different RTC modules on the market, one works off the SPI bus and the other off the I2C bus, well I have both and I never really liked the SPI RCT Clocks, and much prefer the I2C clocks like the DS3231. The SPI clocks I have seem to forget the time, or some random pulse resets the time. Do not know what is the cause, but I ended up ordering more I2C clocks and binning the others.


Wemos D1

Not to be outdone on micro controller usage, I am onto yet another micro that is worth using. I cannot see any real use for say ham radio, but for some other electronics projects i have been tinkering with for way to long, this might just be the go. The Wemos D1 is a uno compatible board that has 1meg flash, 80K ram, 80mhz processor and best of all WIFI, which means i can use this as a webserver for the weather station i have been planning/tinkering/building or procrastinating about for way to long. So with the addition of my other code and the hooking up of some sensors, I should be able to make this thing chooch and display the data on the world wide interwebs.