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Registered Member #8265
Joined: Thu Nov 22 2012, 11:19AM
Location: Australia
Posts: 6
Hi, I have built a 'keyboard' for my drsstc. It is just 8 tactile switches into a pic16f - this part works fine. My problem is that after some protection (opto & oneshot) I have a 4.5V pk output. Evidently this is below the LTP to start my coil - marginally, I think I need at least 5.5V, want 9V. I have tried a 741 with hysteresis set at 3V with 0 & 9V rails. This worked but the output floated at +3-4V, I suspect because the ancient 741 amps need +9V & -9V rails??? I am running everything from a single 9V battery so I can't get -9 and +9V rails for the amp.
- Does anyone know of a common (easy to find) op-amp that can run from 0 and 9V rails? - should the 741 be able to do this? also I thought of(not tried) offset nulling but the 4V seems way to high to be brought down with the offset null??
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
1) If the PIC shares a common supply/ground with the output there is negligible benefit in using opto-isolation, which just adds delays and extra components.
2) I'd run the PIC from the 5v regulator and use something like a TC4421 (because I have some, lower power/cheaper drivers are available) driven directly by the PIC output pin and powered from the battery. (Less parts = better)
Registered Member #8265
Joined: Thu Nov 22 2012, 11:19AM
Location: Australia
Posts: 6
The opto was being used to isolate a midi device (actual keyboard) from the pic - scrapped the actual midi interrupter design because It was making me want to kill myself (could not get anything clean out of the pic-some unknown problem). Went for the simple buttons instead but used the same piece of vero so I just made the opto the input to the discrete logic.
- I have a ucc27222 driver on hand that I will try now, can't see any reason that won't work.
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Increase square wave pk-best op amp
