Simple Signal Generator Project - Page 1
Forum section: electronics / beginners

author: Mkbul
author_rank: Newbie
timestamp: December 12, 2017, 01:43:30 pm
content: Greetings EEVBlog forum,My name's Mike, and I am a 21 year old ECE student in Greece.I am a brand new user to this forum, although I've been a guest for a while. Great to finally be here!Just a disclaimer before I continue, I am really a newbie when it comes to practical things! I've only built the simplest circuits in the lab (basic amplifier configurations, differential amplifiers etc), so please excuse me if my idea/project seems impractical or I haven't accounted for something obvious. I am just building it to gain experience.The idea is the following: I want to build a simple function generator - nothing too fancy, very limited in bandwidth and just the simple waveforms: Square, sawtooth, triangle and sine. I figured the simplest way to do this is to generate the square wave using a 555 timer (discharge it through the same RC circuit so as it has 50% duty cycle, or as close as possible), then pass the result into two integrator op-amp stages to get a triangle form and something that kind of resembles a sine wave (parabola/parabola). I am not sure on how to do the sawtooth wave yet, but I got an idea that involves a transistor acting as a switch on the trangle wave stage. The entire configuration's biased at 0-5V.Now, of course, that's the theory.In practice, I've managed to generate the square wave (has a lot of overshoot and is not perfect, but adequate), but I've ran into a problem when i pass the result into the first integrator. Once the circuit is reset and I begin to measure the voltage, this is what I see:http://prntscr.com/hmgrwvDon't mind the horizontal and vertical axes too much, just inspect the waveform itself. Notice how before the integration begins, there is a very sudden voltage drop. I am not sure why this happens. Do you guys/gals have any idea? Am I missing something ridiculously simple? Also, any suggestions regarding the logic and the project itself are more than welcome!Note 1: I have yet to build proper coupling (and proper biasing), so the waveform just occurs once before i need to reset the capacitor.Note 2: What you see in the image is feed from an Arduino that I use as an oscilloscope. I realise this is not the most trustworthy or flexible of things to do, but I got almost no equipment of any kind due to economic reasons. Been saving money for a few years now, but I am torn between buying an oscilloscope or a telescope, which is my second passion!

author: hexreader
author_rank: Frequent Contributor
timestamp: December 12, 2017, 02:32:43 pm
content: You could just buy this circuit:https://www.velleman.eu/products/view/?country=be&lang=en&id=338491Manual contains schematic.... or if sawtooth is important...Both are hobby toys, but might give you some ideas

author: Mkbul
author_rank: Newbie
timestamp: December 12, 2017, 03:41:55 pm
content: Hello and thanks for the quick reply!I have considered buying one of these circuits, however I realised that I don't actually need it for anything and just buying it won't really help me reach my goal by much. On the other hand, if I sit down and build one like it (or at least a simpler version), I will gain quite a lot of experience building circuits - which is why i've chosen the latter.Once again, thank you for your input!

author: martys
author_rank: Regular Contributor
timestamp: December 12, 2017, 04:48:16 pm
content: Since you don't yet have an oscilloscope, you can see how a simple function generator can be built and used on Youtube.Several videos show good explanations, circuits and waveforms. Just search for "Function Generator".https://www.youtube.com/results?search_query=function+generator+tutorial