A stable negative supply for an op-amp (using 555)
The negative output voltage drops as soon as you connect a load of just a few milliamperes. That's because the negative voltage generator built around the 555 can't supply that much current.

It is a nice proof of concept circuit that shows how voltage inversion can be done in principle, but as you've found out it is not very practical.

There are chips out there designed for voltage inversion that do a much better job than the 555 which is build for timing tasks.

I suggest to order a few ICL7660 style chips. They just need two external capacitors for voltage inversion and will give you a much more stable negative voltage. Also they are more efficient than the 555 based inverter so your battery will live longer.

Beside the ICL7660 there are almost pin compatible alternatives chips you can choose from. They improve upon the ICL7660 in various ways. To name a few:


MAX1044 / TC1044S: Higher switching frequency (e.g. less noise)
LT1054: Higher current, output drops less when loaded. Has internal voltage-regulator feature.