On Wednesday, 3 October 2018 09:16:33 BST Ralph Corderoy wrote: > The `monitor' I was thinking of is a > https://en.wikipedia.org/wiki/Machine_code_monitor and I think your one > is https://en.wikipedia.org/wiki/Resident_monitor
Yes. You are right, the second of those is what I thought of as a Monitor. I suspect the 'Resident' bit was never mentioned. > Terry, what was this 12 V v. 3 V thing you were talking about? Looking > at the schematic through the laptop's lid, I never understood. :-) I was talking about a design that I've been doing for the Model Town to control an Actuator motor from the Pi. There are a number of dedicated chips to do this, but they tend to be low current (eg up to 2A) and bipolar, so the volt-drop across the switched can be as high as 2 V, even when the motor is only consuming a few hundred milliamps. With that in mind we decided to use Power MOSFETs (specifically the IRLZ34NPBF (https://docs-emea.rs-online.com/webdocs/0791/0900766b807913d5.pdf)) because their ON Resistance is very low (about 0.05 Ohms in this case). To drive it we chose the HIP4082IPZ H-Bridge FET Driver (https://docs-emea.rs-online.com/ webdocs/14f5/0900766b814f52f3.pdf). That's the background, now the problem. I built a circuit based on the Application Block Diagram on Page 3, but I couldn't get it to work. To bring the 12 V / 3 V thing into the discussion; the chip can be powered by any voltage between 8.5 V and 15 V and the logic levels have to be less than approx 1 V for a Low and greater than approx 2.7 V for a High. In theory the Pi can do that, although we are aware that we may have to buffer the inputs to get the high level well above the minimum. What I found was that when the Pi put out a high (measured on the LHS of a 100 k limiting resistor), I got 3.3 V (standard Pi High level) and when the Pi put out a low, I got close to 0 V. However, the actual chip pins (RHS of the 100 k resistors) never went below 1 V. In desperation, I laid out a brand new chip on a breadboard, applied 12 V between Vdd and Vss (and nothing else) and measured the inputs. What I got was around 2 V or more. At first I thought the inputs were floating, so I connected the Pi directly, (without the 100 k limiting resistors) and I now have an ex-Pi, so there was current behind the volts. I was asking Paul what he thought because before he moved into IT, he was a hardware engineer. Another ex hardware engineer, ex-colleague of mine has also looked at this and observed the same problem. The problem is that this is simply not what you would expect on the inputs to any logic device! (Or at least what we would expect anyway.) We are still investigating. -- Terry Coles -- Next meeting at *new* venue: Bournemouth, Tuesday, 2018-11-06 20:00 Check if you're replying to the list or the author Meetings, mailing list, IRC, ... http://dorset.lug.org.uk/ New thread, don't hijack: mailto:dorset@mailman.lug.org.uk
