I'll present what I'm doing first. A friend has been having problems with traffic lights and his motorcycle. Complaining about the sensors is a nearly futile endevor here, and the 'workarounds' are not necessarly the best options. After a little thought, I figured I could make the bike seem like it has more metal in it by generating my own field timed to the loop's. I figured I could use a hall effect sensor to sense the flux density over time which I'm hoping will give me a relativly clean waveform, feed that through a differentiator to mimmic Lenz's law, amp it mildly, and feed it through a coil properly oriented so the flux goes through the loop sensor. Since I'm trying to make the prototype with some spare junk I have lying around, I'm trying to design the system for a 741. The problem here is that the powersupply is a unipolar supply. I don't have much experience or education in power conversion, so I'm trying to find out what my options are other than a voltage divier (which will not work well, if at all under load). hile I'm asking questions, I was hoping I could steal a hall effect sensor from an old case fan, but I;m not sure if these are the correct type to do what I want. (trying to find a datasheet from the very few charicters on the package is pretty tough, if not impossible.)
There are chips (eg TLE2426) to split a DC supply, or you can improve on a simple PD using another opamp as a voltage-follower to reduce the source impedance. Headphone amp sites like Headwize should give some info. On Hall Sensors, Ampson A276 is a fairly common type in fans and a datasheet is available for that and a few more.
Better? This is a rough idea at this point. I need to consider the bandwidth of the differentiator because the inductive loops have a range of frequencies that they could be set to. The second op-amp performs the critical inversion, and uses the summing junction to pick out the crossover distortion. It also lets me fiddle with the gain from the integrator. I'm checking out that info cpemma, thanks a lot. As I said, the circuit is really rough, I don't know if I'll get a terribly strong signal off the hall effect sensor, but that can be dealt with using a pre-amp if I need it. I know the push-pull will need to be beefed up. The output transistors will probally need some additional current feeders. I have seen some goods stuff on the DIY audio site, but I never considered looking at sites like that for power supply circuits.
