Discrete NAND Synthesizer Help

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lofiboy

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I know it's possible to create an audible square wave generator using a 4093 or a 7400 by connecting one input to high and the other to ground using a capacitor, then feeding the output back into the grounded input through a resistor.

Not having access to either of these, I made a (working) TTL NAND gate using c2240 transistors running on 6v. I can't, however, make it oscillate.

I assumed it would work because the logic function is identical to that of a 4093, though the IC's design is much more intricate, but I just can't seem to make it work.

When connected to an amplifier, all I hear is uneven crackling. Does the malfunction have something to do with the 7400/4093's totem-pole output (and my circuit's lack of one), my 6v power source, or am I just flat out wrong in my design?
 
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The simple oscillator you are thinking of requires a Schmitt-Trigger gate (inverter) that has hysteresis built in, not a simple logic gate (inverter). You can construct an oscillator using three inverters, see this APP Note.
 
Wow, thanks! I wouldn't have figured that one out very easily. You've saved me a lot of headaches!

I don't have access to ANY IC's in my town, and ordering online means ridiculous shipping costs (upwards of $10 for a 20 cent, quarter oz. IC). Could this three inverter osc be built with discrete components?
 
This is a much better option for a discrete circuit. Sorry to ask another question, but where would the output be taken from?
 
Either (or both) or the transistor collectors.

Re the IC inverter oscillator, they work good with any modern CMOS inverter or inverting gate because the input LO-HI levels have a large hysteresis and are well defined, basically all modern CMOS inputs are "schmidt trigger" inputs.
 
You are misinformed about that.
 
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Perhaps I was thrown off by your stipulation that they are "modern". What do you mean by that? Would you include CD4000 series and 74HC series?
 
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Most of the "newer" CMOS logic made in the last 10 to 15 years have clearly defined hi-lo input levels and excellent stability until they latch after exceeding each level. They are a real step up from the early TTL and early CMOS which had very poor input pin performance, and the modern chips generally have more complex input circuitry, clearly defined LO-HI levels and cleaner faster switching.

All "newer" CMOS gates are fine for making RC inverter oscillators (as the OP asked) and I have used CMOS gates to add oscillators to circuits for many years, and that includes HC ACT etc, although I do buy only brand name CMOS and not weird Chinese knock-offs.
 
OK just make an oscillator out of discrete parts! Why are you trying to make gates out of discrete parts to from an oscillator?
What are you going to use the oscillator for? Andy
 
Roman, I don't dispute that CMOS gates make fine oscillators. I was disputing this statement of yours:
the input LO-HI levels have a large hysteresis and are well defined, basically all modern CMOS inputs are "schmidt trigger" inputs.
Click to expand...
(emphasis mine)
The only CD4000 series gates with input hysteresis that I am aware of are CD4093 and CD40106. Likewise, in the 74HC(T) family, the only ones are 74HC(T)132 and 74HC(T)14. There are lots of other gates in both families, but they don't have Schmitt trigger inputs.
 
Have a look in the databook for the input voltage trigger levels (and the hysteresis);
(all have well defined swithcing levels);
74AC 1.5v 3.5v
74HC 1.0v 3.5v
74HCU 1.0v 4.0v
CD4000 1.0v 4.0v

(these 2 mimic TTL levels but again have very definite switching levels);
74ACT 0.8v 2.0v
74HCT 0.8v 2.0v

CD40106 (hex scmidt trigger); 1.5v 3.5v

You can draw your own conclusions from that. But when using logic ICs in a design I usually hook up a pot to the input and confirm the high and low switching voltage levels, and it's been a lot of years since I've seen any hint of latchup etc when using a slowly changing voltage.

When I designed the Shift1-LCD open-source project I tested a number of CMOS shift registers quite thoroughly and all their inputs stood up well as schmidt trigger type behaviour even when driven constantly with slowly changing RC ramp voltages, which is how the Shift1-LCD works.
 
The above values are guaranteed min/max input switching levels, and have nothing to do with hysteresis.

CD40106 (hex scmidt trigger); 1.5v 3.5v
Click to expand...
These are hysteresis levels, meaning the output will go low when the input rises above 3.5V, and will go back low when the input falls below 1.5V.

Your shift registers may have had Schmitt trigger inputs, but the subject here is gates.
Roman, I'm not trying to make you eat crow. I'm just trying to keep trusting noobs here from being led down the garden path. I repeat - Most CMOS gates do not have Schmitt trigger inputs.
Attached are Vout/Vin transfer curves for a gate without hysteresis (CD4011, 2-input NAND), and a gate with hysteresis (CD4093, 2-input NAND). You can check all the gates in the CD4000 family, and the only other one with hysteresis is CD40106, which is a hex inverter.
 

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Interesting. I don't use a lot of CD4000 series, but I do know all the AC ACT HC etc that I regularly use have quite reliable switching points and hysteresis.

I also have doubts about your first transfer chart for the 4011B, where is it from? I've NEVER seen CMOS gate inputs that had zero hysteresis as shown. Hook one up with a pot on the input and you should see a very obvious hysteresis right around the expected voltages.

From my databook;
BU4011B 1.5 3.5
CD4011B 1.5 3.5
CD4011AE 1.5 3.5
HCC4011BK 1.5 3.5
out of 40 brands and specs listed fo the 4011 there are only about 6 that list 1.0 and 4.0v, the rest are 2.5 and 3.5 which are about the values you always see when testing the real chips.

Now the schmidt version;
BU4093B 1.5 3.5
MC14093BAL 1.5 3.5
again almost all are listed as 1.5v and 3.5v respectively.

It's been a lot of years since I tested a CMOS chip that did not have a large input hysteresis and quite relaible LO and HI threshold voltages. But maybe there are still some crap manufacturers that can't design a CMOS input pin circuit. Can you suggest a brand or chip I can test??
 
Hello Dear Friends, please I was given an assignment to design an 8-bit counter, 7-segment display with given components; TTL 7400N, 7493N family, power source, etc.
We were actually instructed to design and simulate with Electronic Workbench (Multism).
Please, I really need help.
Thanks,
Outlook101
 
I found the same graphs in the Fairchild data sheet of the CD4001BC/CD4011BC.
 
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