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I'm trying to design a simple GAMEPORT to MIDI adapter/cable. However, the original design specifies the 74LS00 which I think is used as a buffer:

http://midi.teragonaudio.com/hardware/pc_intfc.htm

I'm not using Rxd (MIDI IN to the GAMEPORT) so I don't need that side of the circuit.

However, I can't fit the DIP package into the DB15 housing. I did find several SN74LVC1G04 SMD components in a spare parts bag. Can I use two of them together (with the resistors) to accomplish the same function as the 74LS00?

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  • \$\begingroup\$ you need four of them ... one to replace a NAND gate \$\endgroup\$
    – jsotola
    Commented Jan 2, 2022 at 4:59
  • \$\begingroup\$ You probably can but as stated by jsotola you need two of them. The 74LS00 has much more sinking capability on its output then the LVC devices the converse is true the LVC device sources much more current then the 7400. Why not simply replace the 74LS00 with a 74HC00 part that would be the simplest. \$\endgroup\$
    – Gil
    Commented Jan 2, 2022 at 5:05
  • \$\begingroup\$ Ahh, OK. Thanks ... I don't think using four of them will save me any space. How does the 74HC00 help me if I use that instead of the 74LS00? Thanks for the help! \$\endgroup\$
    – SofaKng
    Commented Jan 2, 2022 at 5:14
  • \$\begingroup\$ @SofaKng The 74HC parts are more modern and more likely to be available in surface-mount packages. \$\endgroup\$
    – Hearth
    Commented Jan 2, 2022 at 5:17
  • \$\begingroup\$ An LS part is Low power Schottky, HC is High speed CMOS, the main difference is in the voltage levels they work at. 74LS00 is available in surface mount, there's even a 2 gate version that's 8 pins instead of 14. The other chips you have there should work though, the spec sheet says they work at 5V, and they're rated for +/-50mA output, with the 220 ohm resistor the most it would need to do is 23mA. \$\endgroup\$
    – GodJihyo
    Commented Jan 2, 2022 at 5:22

3 Answers 3

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Yes, you can do that. In your circuit the NAND gates inside the 74LS00 are wired as inverters. You only need two of them so two SN74LVC1G04's will perform the same function. The SN74LVC1G04 can operate on 5 V and has a maximum output current of 32 mA - more than enough for MIDI which only needs 5 mA.

The only problem you might have is if the gameport's MIDI Txd ouput doesn't go above 3.5 V (minimum logic high level for 5 V CMOS). To ensure that it does you could add a 4.7 kΩ pullup resistor from Txd to +5 volts.

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You could use a 74LVC1G86 and ground one of the inputs. It will drive 32mA. You only need one of them if you are not using the Rxd.

However, I would add a 100nF bypass capacitor on the supply and a series resistor on the input (1K or so) and maybe a pullup, though the latter is probably not necessary. CMOS parts are not as robust against ESD as LSTTL and the 1K will help with that.

schematic

simulate this circuit – Schematic created using CircuitLab

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It could work, but it would be slightly non-standard.

Generally a MIDI output is an open drain or open collector output, which means the output is either pulled low or kept floating. An LS TTL chip is not exactly open-collector, but the high output is quite weak. An LVC CMOS chip has much strongrer high output.

So two LCV1G04 inverters would work but the intention is to not to push the wire high, but to let it float.

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