Hex Inverter OSC help. - Page 1
Forum section: electronics / beginners

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 07:01:25 am
content: Hey EEVblog! Total electronics noob here! Only been studying for almost a week now. Been following Dave for years but only recently got into electronics. I decided to follow casperelectronics' OSC tutorial (I'm a synth enthusiast) which only uses a CD40106BE IC, some capacitors, and some resistors/pots! I tried running the output directly to a little speaker I salvaged a while back, but found the oscillation would stop due after a short time to what I assume was the speaker drawing all the current from the IC that would cycle back through the capacitor (could be terrible wrong). I did some research and found that I was to use a buffer circuit. I had a TL074 quad op amp laying around so i slapped that on the breadboard and made a buffer to route the OSC into. Problem is, I'm not getting ANYTHING on the op amp output! Had me baffled and eventually defeated me for the night. If anyone could help me out it would be super appreciated!! As well as some tips to making this a VCO possibly? I'm planning on asking a lot on the forums here. CV, Exponential converters, low pass filters.... all of it I hope to makeP.S. I'm not powering the op amp chip as I do not have a dual power supply. I have 9v batteries I could use to jank one up, but haven't yet. I'm fairly certain the reason it isn't working is because the op amp is not powered. I have tried hooking Vin+ to 9v and Vin- to GND, but still no luck. I know I should learn more about what I'm using but that's why I'm here!EDIT: Uploaded schematic. Vcc = 9v DC

author: spec
author_rank: Frequent Contributor
timestamp: January 10, 2019, 08:00:40 am
content: Hi elizarkCan you tell us about your loudspeaker? On your schematic it is shown as a buzzer which is quite different to a loudspeaker.If it is a loudspeaker can you tell us the impedance (resistance) of your loudspeaker. If the resistance is not marked on the loudspeaker you can measure it with a multimeter set to the low ohms range. The resistance should be in the range 3 Ohms to 32 Ohms.

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 08:13:24 am
content: Cheers for the reply! I'm not at the shop ATM but I believe I read 8ohm on the back of it! I couldn't find anything but buzzers in the EasyEDA libraries. Sincere apologies!

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 09:01:41 am
content: Of course the op-amp must be powered to work.The TL074 doesn't have enough output current drive to power a speaker. You need a power audio amplifier IC. The LM386 is better suited to the job.

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 09:16:41 am
content: Quote from: Zero999 on January 10, 2019, 09:01:41 amI assumed that was the issue. Silly me! Even if I had powered the TL074 with +/- 9v would it not be enough?https://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.htmlThat link above is what I used to make the buffer. If I fed the buffer into another op amp and raised the gain using the equation from that link, would that drive enough current? The speaker I'm using now is from an old Panasonic cassette memo thing. I do plan on wiring a 1/4" jack to run it to a preamp, so would that eliminate the need for anything past the buffer? Sorry, I feel these are basic questions! I hope to learn a LOT from the community!

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 10:08:36 am
content: Quote from: elizark on January 10, 2019, 09:16:41 amThe TL074's output can't output enough current to drive an 8Ω speaker. Increasing the power supply voltage or the gain will not make any difference. You need an IC with a higher output current rating.Look at the graph on the bottom right hand corner of page 21, figure 6, on the TL074 datasheet. It plots the maximum output voltage vs load in kΩ. With a 0.1kΩ load, or 100Ω, the output voltage is under 0.1V, so with an 8Ω speaker it will be virtually zero.http://www.ti.com/lit/ds/symlink/tl072.pdf

author: spec
author_rank: Frequent Contributor
timestamp: January 10, 2019, 12:15:27 pm
content: + elizarkAttached is a schematic for a circuit, using the CD40106 and a couple of transistors, to generate an audio tone from 100Hz to 10KHz. If you have any questions just ask.

author: Audioguru
author_rank: Super Contributor
timestamp: January 10, 2019, 07:37:15 pm
content: The simple oscillator using the CD40106 produces a squarewave output that sounds like a buzzer. Do you want that sound? For a synth you probably want many types of sounds so maybe an oscillator that produces a sinewave is better then it is easy to change to many different types of sounds.

author: spec
author_rank: Frequent Contributor
timestamp: January 10, 2019, 07:57:57 pm
content: Quote from: Audioguru on January 10, 2019, 07:37:15 pmYes, quite true, but the OP wanted to get his Hex Schmidt oscillator working. A synthesizer is a whole different thing.One step at a time.

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 08:47:29 pm
content: Connecting the Schmitt triggers in parallel for more output drive is a good idea, but I have a sneaky suspicion the original poster might want to use all six tuned to different frequencies, so it might not be practical.If the output is taken from the input of the Schmitt trigger, it will be a much nicer sounding sawtooth wave. Of course a high impedance buffer would be required, before the power amplifier to avoid loading the oscillator too much. Reducing the value of R and increasing C in the oscillator circuit will also help to minimise the effects of loading.

author: Circlotron
author_rank: Super Contributor
timestamp: January 10, 2019, 09:00:56 pm
content: The negative (or half rail point) of the power to your opamp must be grounded together with the other ground points on your circuit. Putting 9 volts straight from top to bottom of the opamp will kinda power it but the opamp input and output will have no earth reference so it will not operate very well at all.

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 09:03:45 pm
content: Quote from: Zero999 on January 10, 2019, 10:08:36 amThe dreaded datasheet! Still a bit scared of those, but thank you so much! Definitely helped my fear there. SO much useful info on those graphs!

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 09:05:40 pm
content: Quote from: spec on January 10, 2019, 12:15:27 pmHey spec! Thanks for this circuit! Might as well give it a try and try to learn as much as I can from itTo stop bumping this thread should I ask questions about it in PM?Cheers!

author: elizark
author_rank: Newbie
timestamp: January 10, 2019, 09:10:18 pm
content: Quote from: Audioguru on January 10, 2019, 07:37:15 pmAudioguru! Love the nameEventually I would like to build something like, but I have a ways to go to understand all that. For now, I'm just doing the small things and (trying to) learn hands on.

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 09:59:16 pm
content: Quote from: elizark on January 10, 2019, 09:05:40 pmThe downside with private messages is no one else can help or learn.One way to avoid cluttering up the thread is to respond to several people in one post, by using the Insert quote button, rather than making concurrent posts.I'll post a schematic later, when I've got time.

author: L_Euler
author_rank: Regular Contributor
timestamp: January 10, 2019, 11:21:02 pm
content: In addition to above suggestions, you may want to consider using a couple more of those inverters to further isolate your oscillator. Output of A into B. Output of B into C. A transistor on the output of that op amp would help too. See attached

author: spec
author_rank: Frequent Contributor
timestamp: January 11, 2019, 12:21:38 am
content: Quote from: elizark on January 10, 2019, 09:05:40 pmNo probs elizarkNo, just ask away in open forum that will be fine (I get inundated with PM requests for assistance and am afraid that I simply cannot handle them all)Yes, if you build the circuit of reply #6 and get that working, it will be a good step forward and I suggest good experience . We can then possibly modify it for a better sound, if you want. But, quite honestly, there are much better approaches than using a CD40106 chip.If you are wondering about the five Schmidt inverters in parallel, they isolate the oscillator from the output and together provide sufficient current to drive the output transistors. The CD40106 chip, being a low power CMOS type, does not have much current drive capability.As you are intending to develop a more advanced synth, perhaps you could work on a description and specification of what you want. The highest level decision is whether to use a microcontroller or not.Also, what will the power supply be?

author: spec
author_rank: Frequent Contributor
timestamp: January 11, 2019, 01:31:19 am
content: Quote from: elizark on January 10, 2019, 09:03:45 pmDatasheets can look a bit daunting at first, but they are your best friend in electronics and, when you get familiar with them, they are not that hard. Remember that some of the stuff on a datasheet is either boiler-plate or bull. And a lot of the data is simply not needed for the majority of applications.If you are planning on getting into electronics you must get with datasheets and learn the important parameters for each device type that you would need for normal designs. For example, with opamps, you only need the following parameters:Supply lines max and minInput voltage rangeInput offset voltageInput bias currentOutput voltage swingOutput current capabilityFrequency responseAlso, from the literally thousands of component types available, you only need to stock and know about a relatively few common types to cover most applications. For example, one of the most widely used twin opamps is the LM358. But my goto opamps are the TX711/TX712 and OPA192/OPA2192. The other thing is that many components with different type numbers are either identical or so close that it makes little difference in practice. This is especially the case with BJTs. For example, there are many equivalents to the BC337.This is my list of complementary goto jellybean bipolar junction transistors (BJTs):BC546C/BC556C : 65V, 100mA, 500mW, TO92BC337-40/BC327-40 : 45V, 500mA, 625mW, TO92TIP41C/TIP42C : 100V, 6A, 65W, 2degCW, 150degC TO220TIP35C/TIP36C : 100V, 25A, 125W, 1degCW, 150degC TO2472N3055/MJ2955 : 70V, 15A, 115W, 1.52degCW, 200degC, TO3Note that this is just my goto list, others will have their own lists. But the important thing is to have a list so that you are not swimming around in a sea of different types.Of course you will need specialist components but, if you have a solid base of goto components, you can concentrate on learning about the specialist components, without having to worry about the fundamental goto components. For example when designing, the circuit of reply #6, I didn't need to search for a suitable complementary transistor pair. I just dropped in the BC337/BC327s. And if more power were required, just use the TIP41/TIP42s pair from the goto list.This whole area is part of design (not just electronic) and is known as variety reduction (VR). To take an example you may do a design and calculate that you need a 10nF capacitor here, a 12nF capacitor there and a 70nF capacitor somewhere else. So what you would do is just fit 100nF (goto value) capacitors in all locations. Naturally, some components must have absolute values, the oscillator timing capacitor in reply#6 schematic for example, but in many cases the calculated capacitor values are for minimum values.

author: elizark
author_rank: Newbie
timestamp: January 11, 2019, 03:16:37 am
content: specQuote from: spec on January 11, 2019, 12:21:38 amI have been wanting to build my own modular synth rig for ages now and am only now taking action to attempt to learn electronics. I've gotten a grasp of the molecular level stuff, just not the practical stuff. I plan to go to school to major in electronic engineering since electronics have always fascinated me for my whole life really. If possible I'd want to keep it fully analogue, except for a CV to MIDI module. I've thought about DIY module kits, but I really like to learn EVERYTHING of whats going on in the synths (it just takes me some time to grasp). There is a Youtuber "LOOK MUM NO COMPUTER" who makes his own modules, and even makes tutorials on some, but they are pretty hard to follow. His videos were the main push for me to actually start getting hands on (and Dave's 2 min teardowns of course!). Power supply would probably be +/- 18v but I don't know why, I've just heard that somewhere.I was wondering about why those would be in parallel! By isolate the oscillator from the output, how do you mean? As in act as the buffer? And what do the transistors do exactly? Not SUPER keen on transistors but know the basics, like switching transistors.Quote from: spec on January 11, 2019, 01:31:19 amThanks for this! Definitely adding this to the notes.

author: spec
author_rank: Frequent Contributor
timestamp: January 11, 2019, 07:08:06 am
content: Quote from: elizark on January 11, 2019, 03:16:37 amThat is a fundamentally important area that you have already got but, from what you say, you have a long learning program ahead.Quote from: elizark on January 11, 2019, 03:16:37 amOK analogue it is.Quote from: elizark on January 11, 2019, 03:16:37 am+-18V is often used for high-end audio pre amplifier stages because it gives the largest dynamic range while still staying within the maximum recommended operating voltage of good sounding audio opamps. Will the PSU be mains powered or battery powered or both?Quote from: elizark on January 11, 2019, 03:16:37 amYes, act as buffers so that N1A can get on with its job of oscillating without being affected by the relatively high current of the loudspeaker. The decoupling capacitors help in this too. The combined output from the buffers is around +- 5mA which would not be able to make much volume in the loudspeaker, so the transistors provide more current. Typically BC337/327 would have a current gain (emitter current/base current in this case) of around 100 in that configuration, so that the current available to the speaker would be 5mA * 100 = 500mA. Note that current gain of a BJT is known as HFE and is formally, collector current/base current.But 500mA would be very loud (and there is no volume control) and would soon flatten your 9V battery. The resistor in series with the speaker limits the speaker current to +-75mA.The output at the two transistor emitters will be a square wave of between 1V and 8V which would not be suitable for the speaker. The capacitor in series with the speaker therefore changes this to a square wave of -3V5 to +3V5, which has no DC content and is thus suitable for the speaker.Quote from: elizark on January 11, 2019, 03:16:37 amAfraid that transistors, both BJTs and MOSFETs are the essential active elements of modern electronics. By the way, although transistors can be used as switches, and there are transistors specifically designed for switching, all transistors are analogue.Every integrated circuit, both analogue and digital, is made from transistors, sometimes billions of them. Along with resistors, capacitors, inductors, transformers, and diodes, you need to fully understand how both types of transistor work at the essential level. The good news is that it is not difficult.

author: spec
author_rank: Frequent Contributor
timestamp: January 11, 2019, 09:13:38 am
content: Quote from: elizark on January 10, 2019, 09:16:41 amCould not find an answer to this question of yours: what you say is correct. No audio power amplifier, opamp, or transistors, would be required. But a buffer of some sort would be needed to drive the cable and isolate the synth electronics from the relatively high capacitance and inductance of the cable.The biggest gotcha in any engineering is frequency stability. It is the source of more problems than all other areas put together (just ask a bridge designer). The buffer would also help prevent oscillations with the cable.The buffer in this case would almost certainly be just an opamp.

author: Zero999
author_rank: Super Contributor
timestamp: January 13, 2019, 11:46:07 am
content: Here's the circuit. It's just a proof off concept, not a complete solution.Use one Schmitt trigger oscillator and op-amp for each note and mix them using a passive network of resistors and AC coupling capacitors, before the audio amplifier. The op-amps can be the TL074 or whatever. Three hex Schmitt trigger and four quad op-amp ICs will give 12 notes. If the original poster is still interested, I can provide component values and more information.