Ok, let me figure it out... so i was gonna use the 741, but instead I should use another one with a lower output impedance... I get it, but about the other resistences, do I need to change them? for example the 100kOhms on the right upper corner, wouldn't it drain all the current from my output??
The high resistances are able to be used around an op amp by benefit of it having high input impedances.
Below is a working schematic for what you wish to do. It shows the op amp driving your load directly. It would need to be the type with low output impedance.
The dual oscilloscope traces show the response:
(a) 3.3 V in, +12V out.
(b) 1.65 V in, 0V out.
(c) 0 V in, -12V out.
There are other ways to do the job.
(a) Single 12V supply with an H-bridge. This is 4 transistors/mosfets arranged in a way so that it is possible to send current through your load in either direction.
(b) Bipolar 12V supply with NPN and PNP transistor in a push-pull arrangement.
However the above methods have their problems which must be solved.
- If I have 3.3 in the source - I have 12V on the engine
- If I have 0V in the source - I have -12V on the engine(reverse)
- If I have 1,65 in the source - I have 0 V on the engine (off)
If you want +-12V on the motor then the supply must be more than +-12V. +-15V or +-18V would be good. +-24V is too high; it is too much for a 741 and will waste power.
The circuit below is a bit more complicated than the one shown by BradtheRad, but is also more accurate. The transistors can dissipate up to 1W of heat, so should be mounted on heatsinks.
If you use a power opamp then you do not need the transistors, but the opamp should be mounted on a heatsink.