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View Full Version : I need help with a percussion synth, please


MJay82
Apr15-11, 06:34 PM
Hello everyone. I'm building a few simple percussion synthesizers with a design from "TAB Electronics Guide to Understanding Electricity and Electronics" for my Physics project this semester. This is my first try at building a circuit ever. I am really enjoying the process, but I have a few questions. I hope my questions come across as clear.

1) When multiple "lines" meet together at a junction point in a circuit diagram, this is the equivalent of a "row" on the breadboard - correct? Or to say it another way, components sharing a row act as if they're sharing a common point, right?
1b) Columns share NO connection (the long way), right?

2) The pitch of the drum sound comes from three 1 Mohm potentiometers. These have one pin on one end, and two pins on the other end. I will describe the way that the schematic represents the potentiometer:
There is a point below a "resistor" symbol (jagged line). The point is connected to the jagged line. In addition, there is an arrow emanating from the point, making a square-shape away from the line (wire), then pointing directly back at the jagged line.
My question is this: I don't know which way to orient the potentiometer - where does the one-prong end go, and where does the two-prong end go. The two-prong end on a breadboard is going to end up being on the same row (obviously), so I'm pretty confused as to why there are two ends at all. Obviously I'm not completely clear on how the potentiometer works - and due to time constraints I've got to jump in to this project feet-first.

3) The circuit uses an NTE778A integrated circuit. There is a 1, 2, 3, 4, and 8 coming out of the circuit. This seems self-explanatory, but just to be sure - these numbers indicate what the corresponding numbers on the IC move toward - right?
Number 4 seems to go to -V, and number 8 seems to go to +V (3 goes to ground). Additionally, there is another power source (in the other part of the circuit). So will I just give power to this IC directly then?

I hope someone can help - I have a ton of work I need to do on this project this weekend , but if I can figure out these things by tomorrow, I should be in okay shape. Please ask any questions or tell me if I'm unclear. If it wouldn't be copyright infringement, I could take a picture of the diagram and post it. And I can take a picture of what I've got too, if someone wants to help me spot check. Thanks for any help.

MJay82
Apr16-11, 09:00 PM
I'll post a few pictures in hopes that I just haven't been clear enough.

schip666!
Apr16-11, 09:33 PM
The usual .1" spaced breadboard has 2 rows of 5 or so "pins" connected together on either side of a gap. You can plug an IC into the pins nearest the center gap and then wire up the other 4 pins just like connecting to that IC pin... if that makes any sense ... and, yes, the wires-connected-with-a-dot on the schematic is just like those sets of 5 pins.

There is another common breadboard component layout that usually has two long rows of pins connected by long-row. This is used for power distribution.

Pots generally have a center pin that is the "arrow" in the schematic. That pin can be twiddled anywhere between the two outer pins giving a variable resistance.

Try it all out with an ohm meter and see what's connected to what and what resistances you get.

MJay82
Apr16-11, 10:34 PM
Thanks for helping clear things up a bit, schip!