开云体育

Level Shifting

jerry-KF6VB All Messages By This Member #5993 Hello, This has very little to do with the T41... I have this homebrew linear. It interfaces with my T41 quite nicely. Just like the T41, it has a Teensy 4.1 inside. Bands are chosen using Yaesu "BCD" band codes. Four wires, each one can be "high" or "low" gives you a four bit code and 16 possible bands. The standard is that "high" is near 5V, and "low" is near 0V. Just like in the old TTL days. The Teensies, however are 3.3V devices. Any inconveniences are compensated by the fact that they are WAY faster than any 5V Arduino. When I built the linear, I converted the 5V ( from an FTDX10 ) to 3.3V with a resistive voltage divider. When I built the T41, I converted the 3.3V from the Teensy to 5V using an open-collector transistor switch in each line. The problem with this is that the noise immunity is not good. So when the linear starts transmitting, RF gets into the band-chooser lines. The linear changes to a different band, and the protection circuit then says "Oh you have the wrong LPF", and shuts off the power. I love that protection circuit. I am still on my first MRF1K50. No amount of bypassing fixed it. I have bypassing and RF chokes at the T41, I have bypassing at the linear. I shielded the cable between them. I mostly fixed it by saying "We never change bands during transmit, so ignore those lines at that time". How to know that we're in transmit? Software on the Teensy monitors the drain current of the MRF1K50. If it's greater than zero, we're transmitting. But for some reason, it still does it on 10M if I run more than 800W or so. Doubtless RF starts coming out before the Teensy notices the drain current.... I guess. ANYWAY - the recent discussion about level shifters intrigued me. Is there an IC solution that's better than open-collector drivers and resistive voltage dividers? One that has decent noise immunity? It does not have to be fast; these lines are essentially DC. - Jerry, KF6VB
K9HZ All Messages By This Member #5994 Yes. Use ULN280x parts... I use them for everything where I need to drive stuff... Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: www.VillaGrandPiton.com Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. email:? bill@... toggle quoted message Show quoted text -----Original Message----- From: jerry <jerry@...> Sent: Friday, February 7, 2025 12:19 PM To: [email protected] Cc: K9HZ <bill@...> Subject: Level Shifting Hello, This has very little to do with the T41... I have this homebrew linear. It interfaces with my T41 quite nicely. Just like the T41, it has a Teensy 4.1 inside. Bands are chosen using Yaesu "BCD" band codes. Four wires, each one can be "high" or "low" gives you a four bit code and 16 possible bands. The standard is that "high" is near 5V, and "low" is near 0V. Just like in the old TTL days. The Teensies, however are 3.3V devices. Any inconveniences are compensated by the fact that they are WAY faster than any 5V Arduino. When I built the linear, I converted the 5V ( from an FTDX10 ) to 3.3V with a resistive voltage divider. When I built the T41, I converted the 3.3V from the Teensy to 5V using an open-collector transistor switch in each line. The problem with this is that the noise immunity is not good. So when the linear starts transmitting, RF gets into the band-chooser lines. The linear changes to a different band, and the protection circuit then says "Oh you have the wrong LPF", and shuts off the power. I love that protection circuit. I am still on my first MRF1K50. No amount of bypassing fixed it. I have bypassing and RF chokes at the T41, I have bypassing at the linear. I shielded the cable between them. I mostly fixed it by saying "We never change bands during transmit, so ignore those lines at that time". How to know that we're in transmit? Software on the Teensy monitors the drain current of the MRF1K50. If it's greater than zero, we're transmitting. But for some reason, it still does it on 10M if I run more than 800W or so. Doubtless RF starts coming out before the Teensy notices the drain current.... I guess. ANYWAY - the recent discussion about level shifters intrigued me. Is there an IC solution that's better than open-collector drivers and resistive voltage dividers? One that has decent noise immunity? It does not have to be fast; these lines are essentially DC. - Jerry, KF6VB

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