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Even robot systems occasionally need a negative supply voltage for some purpose or other, and in this kind of application in particular there is a need for an effective circuit that does  not  make  greater demands  then  necessary in terms of current or space. If a low current 5 V supply is needed and only +5 V is available, a natural manufacturer to turn  to  is  Maxim,  and indeed in this case they do not let us down.The best known integrated  circuit made by this company is the MAX232, a level shifter for serial ports with an integrated charge pump that does not need an external inductor. Simple Mini Power Inverter image: Along the same lines, although with a more stable output voltage and higher efficiency, is the MAX660. The device can ‘mirror’ any input voltage between 1.5 V and 5.5 V. With a 5 V input the output is typically –4.7 V with a load of 100 mA. Efficiency at 10 mA is around 96 % and at 100 mA is around 88 %. With an ope...

Small Metronome Circuits Diagram Notes: Q1 & Q2 provide linear frequency operation of IC1 following P1 resistance variation. Q3 was added in order to obtain a louder click, similar to clockwork metronomes. A 12V micro battery was used to obtain a higher output power and more compactness. Rotate P1 fully towards R2, then set R1 to obtain 40 beats per minute (compare with another metronome). Rotate P1 fully towards R3, then set R4 to obtain 208 beats per minute. Finally mark the entire scale with the usual metronome steps, as follows: 40 - 42 - 44 - 46 - 48 - 50 - 52 - 54 - 58 - 60 - 63 - 66 - 69 - 72 - 76 - 80 - 84 - 88 - 92 - 96 - 100 - 104 - 108 - 112 - 116 - 120 - 126 - 132 - 138 - 144 - 152 - 160 - 168 - 176 - 184 - 192 - 200 - 208. Parts: P1______100K    Linear Potentiometer   R1_______10K    1/2W Trimmer Cermet R2_______10K    1/4W Resistor R3______330K    1/4W Resistor R4_______50K    1/2W Trimmer Cermet R5______100K ...