Hello everybody!

It's high time to finish my project. Today, my teacher has seen my project and therefore I would like to make some  summation of my work.

The objective of my project was creating signal generator. At the beginning of my work I had some assumptions - principle of operation, range of generated frequency ...... and other parameters were assumed by me.

Now I can compare final results with this assumptions and comment it.

I think that the most relevant issue is that this device works correctly - is able to generate three signals and I can wireless control it. In my opinion this is some kind of success. Of course, there are also drawbacks, but about them I will write later .

From  electronics point of view all were performed well, because all working. The main problems were connected with quality of generated signals - PWM is frequency non-stable. SAW signal has low maximum frequency. And the sine signal. In sine signal case I have a lot of remarks.

First off all - frequency characteristics - real frequency characteristics are other than simulated, because I have not  used accurate pasive elements - resistors and capacitors. This is main reason different characteristics.
In addition for low frequency signal has flat shape on top. So, I am convince that this issues need more attention - remark for future for young constructors.

Next problem... I did not have enough time, but I made one mistake. Devices such as signal generator require frequency characteristics and comparison real frequency characteristic with simulated. I should have done it. This is very important from using point of view. 

So... I think that this conclusions are satisfied your expectations. Time to say goodbye!

Hardware details.

Hello everybody!

Hello everybody!
During my absent here, I worked on power management system, LP filter and all schematics.
First of all I show You parameters of filter. As I wrote in previous post, my generator will be able to generate sine in following range: 0 - 10 000 Hz. So, filter has passband at 10kHz. More details connected with filter you can see below:

Name: Lowpass,
Multiple Feedback
Chebyshev 0,5 dB
Part: LMH6642MF OA
Order: 6   
Number Of Stages: 3
Gain: 1 V/V ( 0 dB)   
Allowable PassBand Ripple: 1 dB    
Passband Frequency: 10 kHz   
Corner Frequency Attenuation: 0 dB    
Stopband Attenuation: -45 dB    
Stopband Frequency: 18 kHz

The next important issue was checking how this filter works. In this order I used simulation program. Below you can see schematic of this filter and on the oscilloscope you can compare input and output signal.

As you can see filter works correctly - of course in simulation, but I expect that it will be worked correctly on my PCB.
This all about filter. Now I will show you schematics of following parts:
Power management system:

You can see that I obtained two different levels of voltage: 3.3V and 1.65V. This is caused by  operational amplifier which works in single supply mode.

Next picture contains schematic with processor STM32. This issue is  skipped  because this is standard solution for this processor.

 And last picture contains schemat of filter. I think that in this moment all about this topic is enough clear.

So, thank for your attention and you wait for next post.
In next post I will describe communication between generator and PC, I will show you human interface, which I have coded in C#.

The signal generator is still under construction.

Hello.
In previous post I described theory of DDS - now I am going to deal with all connected with construction:
- power,
- communication with PC,
- PCB board,
- etc...

As I wrote in first post, signal generator will be independent device controlled by PC. In last week I created electrical schematic for power and STM32F100. Signal generator will be powered by battery Li-po 3.7V and charged from USB - I will use charger from TI.

Next important issue is communication between PC and SG (signal generator). Communication will be based on modules HMTRP which working on 868MHz. There are modules simply to utilize and enough to my use.

I hope that in next post I will be able to show you picture with results of my work.

Theory! Principle operation of DDS.

It is high time to explain, how my generator will be acted.
So, firstly I would like to tell You something about DDS. What it is?

DDS - Direct Digital Synthesizer is a technique to create different waveform. In fact, this allow  us to generate signal with adjustable frequency. Signal on output is determined by clock frequency and array with data. In essence, the reference clock frequency is “divided down” in a DDS
architecture by the scaling factor set forth in a programmable binary tuning word.
Main adventages of DDS:
- resolution of output signal can be decreased to micro-Hz.
- DDS allow to avoid some problems connected with (i.e.) temperatur which appear in analog     system. 
- better frequency control than in other systems.

... and nothing about drawbacks ;) but there are ...

 Figure 1. Simple Direct Digital Synthesizer

Principle of operation is simply to understand. We have array with sample of sin (one period) in memory. In this case reference osc is a timer. Timer is utilizing to generate interrupt. In this interrupt (on output of DAC) is setting value of next sample from array, where size of steps(jump)  is equal to M. This value defined frequency of signal. 

Figure 2. Digital Phase Wheel

As You can see fo is dependent only on M, bacouse fc and N is always the same (fc is frequency of timer interrupt and N is  a amount of bits each variable in array with data. So, fc/2^n is resolution of output signal. It's very important issue.

I have written above, that output signal is changing in each timer interrupt. So, this leads to phenomena which is shown below:

 

Figure 3. Output signal with/(out) filter.

You can see, that set value on DAC output is keeping by certain time and our signal looks like stairs. To mitigate signal we should use DP filter (red line on picture).

So, this is all for today. Next post will come soon! 

First steps

As I wrote in recent post in this post I would like to describe progress in my activities.
So, let's start.
During the recent week I have worked  on following periferials:
- Digital to analog converter
- USART to communication with PC
- Timer_3 to generating PWM
- Timer_1 to triggering DAC.

Now, I can generate sine or PWM signal by using PC. I have wrote short program in order to set sine frequency or pulse and frequency of PWM.

Below I add picture which show results of my work.

As you see I have to improve quality of sine signal. This signal is obtained directly on on output of processor. I must design analog filter to mitigate edge of generated signal.
Maximum frequency which I obtained  is up to 75 kHz when I sampling this signal with frequency 0.5 MHz.  In this case by using DAC on processor frequency more than 75 kHz is impossible.

Plan for next week:
Firstly I will design analog filter.
I will try start design PCB for this project (maybe only schematics)
I will add more signals ( i.e. triangular)

Introduction

Theme of this blog will be signal generator, which will work based on STM32F100RB. This theme is realized for pass seminary project of Advanced Microcontrollers. Once in week I will attempt to describe progres in my project. Each problem will be solved in other article. If problem is complex I will allocate more articles, which explain yours  doubts.
So, it is high time to started!