Manuals & Schematics– HornBlasters HornBlasters Instruction Manuals and Schematics. Lose your manual or want a digital copy? We got your back! Most manuals are provided in Adobe PDF format only. Electronic Horn - Circuit Schematic Electronic Horn By circuit schematic This is an easy, low cost and easy built circuit of an electronic horn which is designed close to quadruple op-amp IC LM3900 (IC1). IC LM3900 has four independent operational-amplifiers (A1 through A4) having a large output voltage swing.