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# Building a simple oscillator

#### theyreinthehouse

##### New Member
Hi, hopefully this is the right place to post this question. I’m looking to build an oscillator. I have all the parts ready to order and I wanted to double check that I’m not making an obvious mistake. I’m completely new to this and I thought it would be worth a second opinion to know if the parts I found are correct based on the guide I’m following, if anyone has the time to take a look. Any pointers are appreciated.

Here’s a list of the parts based on the guide that I’m following:

1x 1k resistor,
1x 100k resistor,
1x 10k 16mm potentiometer,
1x 2N3904 transistor,
1x LED,
1X 10μF capacitor

And here’s the list of these parts that I’ve found and plan to order:

I’m planning to solder it on this strip board - https://irishelectronics.ie/epages/...ath=/Shops/950018241/Products/2439&Locale=en_ IE

Here’s an illustration of the schematic from the video that I’m following -

##### Well-Known Member
You might want to investigate micros via block programming for a future experience.

Using a $3 Arduino Nano board you can blink an led this easily - You drag the blocks out of middle window into right window, config them, like pick pin number to work with, and mBlock (this free program) generates Arduino code from the blocks and programs the board. So all you have to add is an LED and series R to the pin, do the block programming, and you are in business. Here is a more sophisticated design, but still quite simple to create - Even talking voltmeters become easy as you progress - Lots of fun. Videos on web for learning. Regards, Dana. #### Attachments • 1668551274764.png 153.3 KB · Views: 40 #### AnalogKid ##### Well-Known Member Most Helpful Member My post was made before post #8. Your inference makes no sense unless time travel does. The video link is in #8. I quoted your post #11. ak #### Papabravo ##### Well-Known Member The video link is in #8. I quoted your post #11. ak I was referring to the video in post #1, and the original response was in post #5 #### JimB ##### Super Moderator Most Helpful Member Amidst all the debate about this oscillator, has anyone tried to build it to see if it works? Well, I have. Look here: On the breadboard On the oscilloscope So, in answer to the original query, yes it does work. The components in the OPs parts list are OK, and he has a good chance of it working. My own comments: It is a very simple circuit. I probably would not use it myself unless I needed an oscillator using the minimum of components. Why the LED is there I do not know, it does not seem necessary for operation of the circuit. Variations of the circuit appear on the internet without the LED. JimB #### Tony Stewart ##### Well-Known Member Most Helpful Member This circuit relies on the abrupt breakdown of Veb with V+ on the emitter of the NPN and with the collector on the low side the Vbc is forward biased such that it takes at least 7 or 8 V to Trigger the breakdown. The Not to Exceed Specs would be Vebo=5V + Vcb=0.7 This breakdown comes fast like a unijunction and a DIAC or an SCR, except in a tiny junction that cannot afford much current before the peak energy density causes physical damage in reverse breakdown mode. It works well but with severe current limitations. 3 CMOS inverters or 1 Schmitt inverter may work down to 3V and be more reliable. Last edited: #### rjenkinsgb ##### Well-Known Member Most Helpful Member This circuit relies on the abrupt breakdown of Veb with V+ on the emitter of the NPN and with the collector on the low side the Vbc is forward biased Thanks, that's confirming what I said back in post #4, with the more detailed specifications on the device voltages etc.. It's a very neat and ingenious novelty, but definitely not an oscillator circuit I'd ever consider using for anything practical or that needed any reliability. As I said then: There are many others that are more reliable and more predictable! #### theyreinthehouse ##### New Member My post was made before post #8. Your inference makes no sense unless time travel does. No it wasn’t. Your first post was made before post #8 but your second post, where you called the video bogus, was afterwards. The other commenter referred to you saying it was bogus so they’re not talking about your first post. No time travel required. #### theyreinthehouse ##### New Member This circuit relies on the abrupt breakdown of Veb with V+ on the emitter of the NPN and with the collector on the low side the Vbc is forward biased such that it takes at least 7 or 8 V to Trigger the breakdown. The Not to Exceed Specs would be Vebo=5V + Vcb=0.7 This breakdown comes fast like a unijunction and a DIAC or an SCR, except in a tiny junction that cannot afford much current before the peak energy density causes physical damage in reverse breakdown mode. It works well but with severe current limitations. 3 CMOS inverters or 1 Schmitt inverter may work down to 3V and be more reliable. Thanks a lot for the feedback! I don’t understand much of what you said but I doubt I will be using this for much of anything, other than to just try and make it and get it to work. So hopefully its reliability as part of a bigger project of some kind won’t come into it for me. #### theyreinthehouse ##### New Member Amidst all the debate about this oscillator, has anyone tried to build it to see if it works? Well, I have. Look here: On the breadboard View attachment 139320 On the oscilloscope View attachment 139321 So, in answer to the original query, yes it does work. The components in the OPs parts list are OK, and he has a good chance of it working. My own comments: It is a very simple circuit. I probably would not use it myself unless I needed an oscillator using the minimum of components. Why the LED is there I do not know, it does not seem necessary for operation of the circuit. Variations of the circuit appear on the internet without the LED. JimB Wow thank you for checking it out. I really appreciate that! When you said the parts list was OK, did you mean my list of links to the parts I plan to order was correct or the list above that which came from the instructions I was using to find the parts? I just want to know that I found the right parts to order online so as not find out my mistake later when attempting to get this to work. Thanks again. #### theyreinthehouse ##### New Member You might want to investigate micros via block programming for a future experience. Using a$3 Arduino Nano board you can blink an led this easily -

View attachment 139316

You drag the blocks out of middle window into right window, config them, like
pick pin number to work with, and mBlock (this free program) generates Arduino
code from the blocks and programs the board. So all you have to add is an LED
and series R to the pin, do the block programming, and you are in business.

Here is a more sophisticated design, but still quite simple to create -

Even talking voltmeters become easy as you progress -

Lots of fun. Videos on web for learning.

Regards, Dana.
Oh nice one. I’ll look into this today. That looks like a great way to start learning. Thanks for showing me that.

#### JimB

##### Super Moderator
When you said the parts list was OK, did you mean my list of links to the parts I plan to order was correct or the list above that which came from the instructions I was using to find the parts?

I looked at the links and the components in them seemed to be OK.

JimB

#### Ian Rogers

##### User Extraordinaire
Forum Supporter
I looked at the links and the components in them seemed to be OK.

JimB
Well done.. You drink my cup of tea!!

When I look at the "neon" version, It MUST do something similar!! Crack on Jim...

##### Well-Known Member
Oh nice one. I’ll look into this today. That looks like a great way to start learning. Thanks for showing me that.

Main site -

Scratch for Arduino (once you learn one block language the others very similar) -

Regards, Dana.

#### AnalogKid

##### Well-Known Member
Amidst all the debate about this oscillator, has anyone tried to build it to see if it works?
I did, sometime last year. A friend has a piece of old test equipment powered by two 9 V batteries, kept forgetting to turn it off, and was moaning about having to stop whatever he was doing and replace the batteries when he needed it again.

A nice thing about this circuit is that it gets double duty out of the energy it consumes. The current that goes into the timing capacitor is then dumped through the LED to illuminate it. This makes the circuit more efficient than a typical 2-transistor multivibrator driving an LED. National Semiconductor did something similar in the now-obsolete LM3909.

ak

#### JimB

##### Super Moderator
Amidst all the debate about this oscillator, has anyone tried to build it to see if it works?
I did, sometime last year.
OK, but I was thinking in terms of building the circuit as posted by the OP.

The OPs circuit significantly different from the one shown in your link in post #17 with regard to the connection of the LED.

The current that goes into the timing capacitor is then dumped through the LED to illuminate it.
That statement had me scratching my head for a minute until I saw the connection in the link in post #17.
That circuit would make a nice simple slow LED flasher circuit.

JimB

#### AnalogKid

##### Well-Known Member
That statement had me scratching my head for a minute until I saw the connection in the link in post #17.
That circuit would make a nice simple slow LED flasher circuit.

JimB
Sorry - should have been more clear.

To the OP: The schematic in post #1 is a variation I have not seen before. It will produce a pseudo-sawtooth output, but the transistor is applying what is effectively a dead short across the capacitor each cycle. The energy stored in the capacitor is dissipated in the transistor as heat, without going through the LED. Moving the cap's - pin (cathode) connection to GND routes the cap's discharge current through the LED for a short bright blink.

ak

#### Tony Stewart

##### Well-Known Member
When using BJT's keep in mind the base current must be at least 3% of the collector current as hFE drops to near 10% of it's value at rated saturation but actually rated at Ic/Ib=10 typically and 50 best case (\$) Where as a 1 Ohm FET does not have that issue so smaller caps and much greater R values are possible for slow pulsing. Keep in mind duty cycle might not be 50% unless ratios are optimized.

https://tinyurl.com/22on3n6l

Here's a few different options.

#### Tony Stewart

##### Well-Known Member
I don't recall you saying what the load is for Audio out. If you intend to use Line input that might be 10k 1Vrms max.

There is no need for 12 to 18V when all you need is 9V such as a battery. You could also bring out 0, 5V supply from a PC https://tinyurl.com/2o7ap8n5 from a Molex connector. Red/Blk

#### AnalogKid

##### Well-Known Member
There is no need for 12 to 18V when all you need is 9V such as a battery.
The circuits in posts #1 and #8 (the original question), and #17 (a variation) will not operate on 9 V.

ak

#### AnalogKid

##### Well-Known Member
When using BJT's keep in mind the base current must be at least 3% of the collector current
For other circuits, probably. For the OP circuit, there is no (traditional) base current.

ak

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