Hex Inverter Midi Driver for Wireless

Thread Starter

Bellows

Joined Jan 20, 2018
13
I am attempting to mimic a midi driver that uses a TI LS05 hex inverter to drive a wireless transmitter for a midi data stream from a digital accordion controller to the off-board module (commercial brand is Millennium, Version 4.0). It is my goal to convert a Version 3.X Millennium to become wireless.

I am having difficulty to select the correct hex inverter. I don't know much about TTL design. I first used an NTE777 hex inverter from Fry's. The wireless system drops some of the pulses in the midi/UART data stream. Then i built a circuit with a SN7416 open collector. It still drops pulses from the stream (observed with a DSO). It appears that my driver does not provide a good high level to the wireless, which then fails to "see" some of the pulses. The circuit is the same. The components are different, i.e. primarily the hex inverter. My driver output reaches only 4.0 V for the high level, whereas the LS05 in the Version 4 provides a full 5.0 volts. I strongly suspect this is the problem.

I am having trouble finding an LS05 in small quantity. Many variations. Samples available are for surface mount (which is the original design), not for my breadboard. And, for that matter, not sure which LS05 to use....there are several. Can someone give me some guidance or recommend which equivalent hex inverter chip to use to mimic the LS05 from TI? Or, can I pull up the output of the second inverter with a resistor (there is no pullup on the output in either design)?

Added information: When I bypass the wireless system and hardwire my prototype driver in the Version 3 directly to the accordions off-board module, it works fine. It is the wireless system that drops pulses. Of course, in the hard wired case, there is no transmitter in the loop and the level requirements are different. It is the wireless transmitter that doesn't pass along the pulses when the high level is only 4 V. But the same transmitter works fine in the Version 4.0 controller where the driver provides 5.0 volt high levels. Los levels are identical in both cases.
 

danadak

Joined Mar 10, 2018
4,057
Spec sheets or part number on device(s) driving the inverter and the transmitter
the inverter is driving ?

Regards, Dana.
 

Thread Starter

Bellows

Joined Jan 20, 2018
13
The inverter is driven by chip without markings. Schematic is poor quality. Looks like HIC16C74. Not sure about the 'H'. Pin 25 of this chip drives the inverter in both controllers. Suspect it's a CMOS EPROM. Power supply is regulated 5 volts.

The inverter drives a MidiJet Pro wireless system. Manual attached - no real specs, though. Vendor will not disclose schematic...say it's proprietary. I might be able to trace what the hex driver connects to internally, but don't have that at hand.

Am measuring and documenting the levels coming out of the hex inverters in both systems. Suspect different levels coming out of the hex inverters in the two systems. Need to confirm. Transmitter requires a midi input differential >1.8 volts, or stops recognizing pulses. Strange that the pulses coming out of the receiver have different pulse widths than those going into the transmitter.
 

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