TL081, OP07, CA3140 and TL084 on +-12 V
Four op-amps follow one knob from -12 V to +12 V: the TL081 and TL084 stop 1.5 V from each rail, the OP07 2 V, and the CA3140 reaches down to 0.13 V of -12 V. There is no microcontroller in it: the simulator solves the 9 parts as a circuit, so it runs the moment you press Run, and nothing needs compiling.
Teaching? Assign it to your class in one click.
Intermediate About 20 minutes to build and run. Runs in your browser. Free, and no account needed.
The parts retail for about $8.20. On Mokxi they're free.
What you'll learn
- Output swing limits of different op-amp types
- Followers on split supplies
- Reading datasheet headroom in a real circuit
- Pinouts differ between chips
- Difficulty: Intermediate
- Time: About 20 minutes
- Parts: 11
How it works
Four op-amps are wired as followers of one knob that runs from minus 12 V to plus 12 V. Each output is copied back to its own inverting input. Four meters read the outputs, left to right: TL081, OP07, CA3140 and TL084.
In the middle they all agree. At the ends they stop short of the supply in different ways. The TL081 and TL084 stop 1.5 V from each rail. The OP07 stops 2 V from both. The CA3140 stops 2 V under the top but gets within 0.13 V of the bottom rail.
The TL084 is four TL081s in one chip.
Parts list
11 parts, plus the jumper wires and 4 bench instruments. The parts retail for about $8.20; on Mokxi they're free, and so are the instruments.
- 1 × Full-size breadboard
- 2 × Power, 12 V
- 1 × PotentiometerIn Halloween Prop Kit, Starter Projects Kit.
- 3 × Power, -12 V
- 1 × TL081 JFET op-amp
- 4 × Multimeter
- 1 × OP07 precision op-amp
- 1 × CA3140 BiMOS op-amp
- 1 × TL084 quad JFET op-amp
Wiring table
Every connection, pin by pin, read from the circuit itself. Each row joins the pin on the left to the pin on the right, by a jumper wire or a breadboard strip.
| Part and pin | Connects to |
|---|---|
| Potentiometer pin 1 | 12 V |
| TL081 JFET op-amp pin VCC+ | 12 V |
| OP07 precision op-amp pin V+ | 12 V |
| CA3140 BiMOS op-amp pin V+ | 12 V |
| Multimeter (1) pin COM | Ground |
| Multimeter (2) pin COM | Ground |
| Multimeter (3) pin COM | Ground |
| Multimeter (4) pin COM | Ground |
| TL081 JFET op-amp pin IN+ | Potentiometer pin 2 |
| OP07 precision op-amp pin IN+ | Potentiometer pin 2 |
| CA3140 BiMOS op-amp pin IN+ | Potentiometer pin 2 |
| TL084 quad JFET op-amp pin 1IN+ | Potentiometer pin 2 |
| Potentiometer pin 3 | -12 V |
| TL081 JFET op-amp pin VCC- | -12 V |
| OP07 precision op-amp pin V- | -12 V |
| CA3140 BiMOS op-amp pin V- | -12 V |
| TL081 JFET op-amp pin OUT | TL081 JFET op-amp pin IN- |
| Multimeter (1) pin V | TL081 JFET op-amp pin IN- |
| OP07 precision op-amp pin OUT | OP07 precision op-amp pin IN- |
| Multimeter (2) pin V | OP07 precision op-amp pin IN- |
| CA3140 BiMOS op-amp pin OUT | CA3140 BiMOS op-amp pin IN- |
| Multimeter (3) pin V | CA3140 BiMOS op-amp pin IN- |
| TL084 quad JFET op-amp pin 1IN- | TL084 quad JFET op-amp pin 1OUT |
| Multimeter (4) pin V | TL084 quad JFET op-amp pin 1OUT |
| TL084 quad JFET op-amp pin VCC+ | 12 V |
| TL084 quad JFET op-amp pin VCC- | -12 V |
The notes that come with it
There is no microcontroller in this one, so nothing is compiled: the simulator solves the circuit itself. The file in the editor is the notes that come with it.
// A TL081, an OP07, a CA3140 and a TL084 on +12 V and -12 V, each a
// follower of one knob.
//
// The knob runs from -12 V to +12 V. The meters read the four outputs, left
// to right. Turn it to each end:
//
// knob at +12 V knob at -12 V
// TL081 10.50 V -10.50 V 1.5 V from both rails
// OP07 9.99 V -9.99 V 2 V from both rails
// CA3140 9.99 V -11.87 V 2 V under the top, 0.13 V over the bottom
// TL084 10.50 V -10.50 V four TL081s in one chip
//
// The CA3140 is the odd one: its output reaches down to its negative supply,
// so on a single supply it can come down to ground, where the others cannot.
//
// The singles have the 741's pinout: IN- on pin 2, IN+ on pin 3, V- on pin 4,
// OUT on pin 6, V+ on pin 7. The TL084 has its V+ on pin 4 and V- on pin 11,
// so here it gets a +12 V and a -12 V source of its own in those columns.
Troubleshooting
The usual mistakes with this circuit, and the fix for each.
- A meter reads 0 V This project
Check that op-amp's supply pins. The TL084 has V+ on pin 4 and V- on pin 11, unlike the single op-amps. - Outputs reach the full 12 V This project
Not possible. Each op-amp stops short of its rails, so if one reads 12 V, check the wiring. - The reading jumps around or only covers part of the range. Potentiometer
Wire the two outer legs to 5 V and ground and the middle leg (the wiper) to an analog pin. Using the wrong two legs gives a dead or partial range. - Turning the knob does nothing, or the value is stuck at 0 or 1023. Potentiometer
Check that the wiper goes to an analog input (A0 to A5 on an Uno), not a digital pin. Make sure both ends are connected, since a floating end gives noise. - The output swings to one rail, or distorts. TL081 JFET op-amp
The TL081 wants a split supply, such as plus and minus 12 V, and needs a few volts of headroom. Use a rail to rail op-amp for a 5 V single supply, since it will not run well there. - The pinout is confused. TL081 JFET op-amp
It uses the 741 pinout in a DIP-8: pin 2 is the inverting input, pin 3 the non-inverting, pin 6 the output, pin 7 V plus and pin 4 V minus. Pins 1 and 5 are offset null, left open. - The reading is zero, negative or nonsense when measuring voltage. Multimeter
Set the dial to volts first, then touch the probes across the part, in parallel. Red goes to the more positive point. A negative number just means the probes are swapped. - Measuring current gives zero or blows the meter's fuse. Multimeter
Current must flow through the meter, so break the circuit and put the meter in series. Never put an amps setting straight across a supply. Start with the highest current range.
Change it and keep it
Open it in the editor, change the circuit or the code, and keep your version in a free account.