Author Options:

(You probably get these all of the time) I need help with a schematic! Answered

I'm sure the instructables community is going to facepalm when seeing this, but here I go. I wanted to make this http://www.apogeekits.com/images/lie_detector.gif. It is a lie detector that is supposed to be done using a kit. However I wanted to try my hands at breadboarding so bought all the parts and a breadboard instead. I have looked everywhere, and all I am able to find are indexes of common schematic terms or pictures. If anyone would be willing to help me I would be forever grateful. I have knowledge on how to use a breadboard, and I have made simple LED circuits using a resistor. But when you start having to connect multiple parts to a bus I get lost. Thanks in advance!



Best Answer 7 years ago

It sounds as though your question is on basic breadboarding. A breadboard such as the one at https://www.instructables.com/id/Breadboards-for-Beginners/ allows multiple connections to a single lead of a single component. And as long as there is a direct connection, it doesn't matter exactly where that connection is made.

The + bus on the left of that breadboard has 50 holes all connected.  The - bus, likewise.  It is convenient to plug the + end of your power supply or battery into one of the + holes.  R1, TR1, L1, and L2 each can be plugged into the breadboard, and jumper wires used to connect each to the + bus.

Likewise, two leads of VR1, and R4, R3, C1, R2, and one probe all are connected to a - bus by jumpers.

Of course, you can also plug the appropriate lead of each of these components directly in to the appropriate bus.

Hope this helps.

Didnt think of it like that. Ill try that!

I still have had no luck getting it to work properly... I am positive I am using all the right parts. Quadrupole checked...

It's really a matter of working at it in a methodical way and laying out the components so you need the minimum number of wire links. Something which would help is a free program called PEBBLE which will allow you to design the layout on screen before you start plugging things in.Just download it (slow server), copy the Pebble directory out of the zip file and click the 'pebble.htm' file.
The resistors and capacitors can go in either way around.  The LEDs you already know about and you'll have to Google for the pinouts for your transistors - just enter the transistor number with 'datasheet' after it to get the information.  The pinouts will be near the top of the document and be labelled E C and B for emitter, collector and base. 

Post back here if you need more specific advice.

Oh sorry. I am pretty steady on the components and how the work. It actually putting them on the board that confuses me. Ill try out PEBBLE now.

As long as all the right connections are made, layout on the board doesn't matter much at the frequencies you're usually going to be dealing with.

Right but for example, no the schematic there is a variable resistor at 100uf Capacitor, and I honestly can't tell what to connect that to in relation with the parts it is supposed to connect to

The variable resistor (VR1) has one end and its center (variable) connection attached to V-. The other side connects to the base of TR2 and to one side of R5. I presume you can see where the other side of R3 connects.

(The little loop in the wire which crosses this one means "not electrically connected". There are several ways of representing that.)

Does that help?

There is still something I dont understand, and it is basically connections. I get that a loop over thing means not electrically connected, but some components seem to have to connect to 4 different things. My biggest problem being the 100uf Capacitor. From the schematic it looks as if it connects to both 1M resistors, the ground of Transistor 1, and the 10k Resistor! Is this true?

The top end of the capacitor (it's 100nF, not 100uF) connects to both 1M resistors, the BASE of TR1 and one of the probe leads.

The bottom end of the capacitor connects to the other probe, the other end of one of the 1M resistors, the 10K and 470R resistors, one end of the track and the wiper of the pot and the negative of the battery.
This is called the 'negative rail', or '0V rail'.  If you're using the type of breadboard with a connected line of holes along the top, and a connected line of holes along the bottom, you' connect the bottom hole line to the negative of the battery.  (And the positive of the battery to the top line - the 'positive rail'.)

Have you tried Pebble?  Does your breadboard look like the simple one which comes up when you start it?  On that one the top horizontal row of holes are connected and will be the positive rail and the bottom row of holes will be the 0V rail. 
Each group of 5 vertical holes are also connected, (e.g.A1,B1,C1,D1,E1), and this group is not connected to anywhere else.  The gap in the middle is to allow the board to be used for an IC as well.

Is your breadboard one you solder to or the type you push in component legs and wire links?  Can you give a link to a picture of it?

My breadboard looks like this! http://www.hiviz.com/kits/instructions/images/bb_002.jpg

Honestly if anyone wants to show me an actual PEBBLE made version of this would help a ton!

It is common in circuits for multiple things to be connected, rather than always pairwise. There's nothing wrong with that.

One end of C1 is wired to one of the probes, and to one end of both R1 and R2.

The other end of C1 connects to the other probe, the other end of R2, one end of R3, one end of R4, one end and the middle of VR1, and the negative terminal of the battery.

If there's a line, there's a connection -- either directly or via a wire. The circuit could be built to look exactly like the schematic diagram, with the lines being wires and the component symbols replaces with the actual component, and it would work. It doesn't have to be laid out exactly that way -- the schematic is arranged for maximum readability, and when building the thing you can shorten, stretch, or bend wires as necessary for the space you're fitting the circuit into -- but topologically, the schematic really does describe what you want to build.

(At higher frequencies, component location and wire routing starts to be important. Not for this circuit.)