Above is the design of the RCD programmer. It can be found at the site of Feng3 (Three is pronounced 'san' in Japanese so it should be Feng San): feng3.cool.ne.jp/en/rcd Oh Feng charges his main capacitor in the negative TxD phase and when he turns TxD positive, the voltage is roughly doubled so this design will work with laptops and similar which have +/- 7 Volts RS 232 levels. Operation is rather straightforward. But Feng took better care of protecting RB6 and RB7 by means of the diodes D1 .. D4. RB7 feedback is done without a transistor. It seems to work. This would be my preferred design, to be honest.