(information and design by Norbert).
Cassette interface for the Micro-KIM.
With small changes Norbert took the circuit described in the 3rd book of Elektor Junior computer. The +12 V problem he solved taking a LT1073 dc/dc converter to generate this voltage. Everything is working fine: Micro-KIM is connected to the soundcard of the computer to store and reload programs.
N39 is needed because there is not a port present or reachable on the Micro-KIM board, so it takes 1/4 74LS01. With a pullup resistor of 3k9 connect the unused inputs to +5V, so the whole thing will not oscillate.
For the +12 V generation a LT1073 CN8-5 was used. The diagram is shown on page 12 of http://www.datasheetcatalog.com/datasheets_pdf/L/T/1/0/LT1073.shtml (5V to 15V Step-Up Converter). It is important to use exactly the values of the resistors (metal oxid series) shown there. The LT1073 CN8-5 is presently still available for 4,20? at www.reichelt.de . They also have got the LT1073 CN8, but it did not work in this context. The no-load voltage measured at the output of the LT1073 is much higher (arround +40V) than the desired +12V. But with load it reduces to about +11.8 V and remains constant there. A 12V/1W zener diode protects the 12V output of the LT1073.
