The transistors quoted, 2N2222A, are not critical. Any general-purpose transistors will do. I have drawers full of various types including BC107, BC108 and BC10 11211d311l 9. I built the above circuit using BC109 types and it works great.
The four capacitors (called pump capacitors) connected to the MAX232-CPE are dependant on the model of MAX232 you buy. The MAX232-ACPE is a "higher speed" device which can use 0.1uF capacitors, this should reduce the size of your interface but the chip is about $5.00 per unit as apposed to $2.00 for the MAX232-CPE.
The MAX-232-ECPE is the Electrostatic Discharge Resistant model, therefore it's more robust and it's about $3.00 per chip.
The MAX232-EPE is the high temperature version of the -CPE chip, and it's about $3.00 per chip as well.
The MAX233-CPP is the "standard" no external capacitor model, and it's about $7.50 a chip.
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