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This link https://www.efxkits.us/square-wave-generator-circuit-using-op-amp/ describes a nearly identical project and contains a more detailed schematic. I've included that schematic here, in case the link goes bad in the future. It refers to the LM1458 op amp, but I suspect than the LM324 can also be used. The LM324 is getting on in years now and there are better ones, but one of the advantages of the LM324 is that it's cheap and can be powered by a single source. I've been using the MC34074AP as a plug-in replacement for the LM324 and have been very happy with it.