breadboard issues?

jptck · Posted: Fri Dec 11, 2015 3:14 pm Post subject: breadboard issues?

hey all, i'm new here! i've really enjoyed lurking thus far. this is an amazing community. y'all are brilliant and kind to each other.

i'm just getting started in the world of lunettas. have self-taught basic concepts in electronics, and improved my soldering skills through circuit bending exploits.

recently, i've been playing around with 4093 / 40106 type oscillators. i'm running off a 9V battery and feeding the oscillators into a simple LM386 based amplifier on the same bus (decoupled with 100uF). all is set up on a cheap breadboard.

frustratingly, i'm having some issues which I'm tempted to chalk up to parasitic effects on the breadboard. i've tried decoupling caps + tying unused inputs to ground. still, the circuit performs unreliably. specifically i'm trying to chain three 4093 gates to achieve a sort of pulsed chirp effect (~1 Hz gating ~5 Hz gating audio rate oscillator). all works fine when the final, audio rate oscillator is at higher frequencies, but things break down when i drop down to lower frequencies. i will diagram the intended vs observed output:

x = tone at, say, 440Hz

intended
x x x x x [silent] x x x x x [silent] ...

observed
x x x x x [sustained tone x] x x x x x [sustained tone x] ...

i'm wondering if any of y'all have ever run into issues when prototyping logic circuits on the breadboard, and how these sorts of issues might be mitigated. is it worth investing in a better breadboard? should i just start building on stripboard?

jptck · Posted: Fri Dec 11, 2015 3:19 pm Post subject:

i also have questions about which DIY amp designs are best suited to lunettas (smokey? lil gem? coupling capacitors? gain?), but perhaps this should be its own post.

trav · Posted: Fri Dec 11, 2015 4:06 pm Post subject:

Looks like your 5 Hz gate is "on" during the [bit between brackets]. Freq could be determining whether that gate halts on a 0 or a 1? Just a guess; posting a schematic would help.

Would it be easier to have the 5 Hz and 1 Hz oscs running separately, use the spare gate on the chip to (N)AND them together, then use this to control the audio rate osc?

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jptck · Posted: Sat Dec 12, 2015 12:36 pm Post subject:

you were absolutely right, trav! thank you.

i knew that tying one of the inputs of a NAND oscillator to ground effectively "shuts off" the oscillation. i forgot that in this deactivated state, the output is held HIGH. this makes it a bit trickier than i was anticipating to chain a few oscillators together - at least, the way i wanted to. contrary to my hopes and expectations, when an oscillator's "gate input" goes LOW, this state doesn't propogate downstream in shutting off all subsequent oscillators.

it is kind of strange that my circuit behaved differently depending on whether the final oscillator was pitched higher or lower...

but enough talk, i'm posting a few diagrams to further clarify things.

EDIT: i didn't see your schematic before posting. that seems like it might work better for me! thank you! look forward to trying it out.

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synaesthesia · Posted: Sat Dec 12, 2015 3:19 pm Post subject:

Regarding amplifier circuits, if you want a simple circuit and need to drive 1W speakers, there are plenty of integrated power amplifier ICs available like the popular LM386 or the TDA2822. If all you need is to drive a small speaker, the following two circuits are excellent for that task. The left one is really simple and good enough for digital signals like a square wave or PWM output from a micro-controller. The right one is great for analog signals, has a high gain, and is my favorite. You can find it at the Talking Electronics web site as Fig. 27a.

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jptck · Posted: Sun Dec 13, 2015 12:00 pm Post subject:

thanks, synaesthesia!

indeed, i am just driving a small speaker. for some reason, i'd been fixating on using the LM386 - i wanted "simple," and this chip is just so ubiquitous in basic audio amp applications. also, it's on the LooneyBoard!

not sure why i didn't think to just use a couple transistors! going to try both of these out (btw: i loooove the Talking Electronics site).

do you happen to know anything about how much power either of these setups would consume? i know the LM386 burns through 9Vs pretty quickly, but i don't know quite enough about electronics yet to take an educated stab at this question.

umschmitt · Posted: Wed Dec 23, 2015 8:20 am Post subject:

Aaaaand i'll take these two amp circuits home too! Thanks a bunch.