Ikrananka Posted February 7, 2019 Share Posted February 7, 2019 (edited) I have previously completed a pause mod on one of my CVs and am now planning on doing this again for another. This involves placing a switch on the system that when switched to pause pulls pin 24 (WAIT) of the Z80 CPU low (ground). However, this time I'd like to have an LED illuminate when the system is paused. I have a low understanding of electronics and so am looking for some help on how to achieve this. Would the following work? I have a specific switch in mind so I need to be able to do this with a single pole switch as shown. Edited February 7, 2019 by Ikrananka Quote Link to comment Share on other sites More sharing options...
Osgeld Posted February 7, 2019 Share Posted February 7, 2019 Put a resistor before or after the led 330ohm or more Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 8, 2019 Author Share Posted February 8, 2019 Put a resistor before or after the led 330ohm or more Thanks. So, something like this. When not paused will the LED part of the circuit interfere with the Z80 WAIT line?: Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted February 8, 2019 Share Posted February 8, 2019 (edited) Keep using +5V This may give you an interesting result though. The M1 state pulls the WAIT pin down for a clock cycle, as does the sound chip. So I think you'll see the LED on all the time, though dimmer when not paused. It might be simpler to use a switch with an integrated LED (well, I *think* they exist), or otherwise use a DPST or DPDT switch and have the LED on the other pole. Edited February 8, 2019 by ChildOfCv Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted February 8, 2019 Share Posted February 8, 2019 Another suggestion is to experiment with using the BUSRQ line instead of the WAIT line. BUSRQ not only tells the processor to sit tight, but it also tells the processor to completely disengage control of the data and address buses. So it's WAIT on steroids. And it's a line that's unused except for the possibility of expansion units such as the Atari module. Quote Link to comment Share on other sites More sharing options...
omf Posted February 8, 2019 Share Posted February 8, 2019 you could do it like that yes but i would isolate the LED from WAIT with a double pole double throw switch. have one side of the switch for WAIT and one side for the led connecting to +5 via a 220 or 330 ohm resistor, you could use a higher value depending on the LED brightness you want to achieve, you will have to experiment on the brightness you want to use Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 8, 2019 Author Share Posted February 8, 2019 you could do it like that yes but i would isolate the LED from WAIT with a double pole double throw switch. have one side of the switch for WAIT and one side for the led connecting to +5 via a 220 or 330 ohm resistor, you could use a higher value depending on the LED brightness you want to achieve, you will have to experiment on the brightness you want to use I have a specific DPDT switch I'll be using for this but the other pole will be used to turn off the sound when the system is paused. Hence my desire to try and pause the system and illuminate the LED with a single pole. Quote Link to comment Share on other sites More sharing options...
SiLic0ne t0aD Posted February 9, 2019 Share Posted February 9, 2019 Parkfun and I did some experiments with this a couple years ago.. He made a nice drawing of the pause mod w/sound off circuit and took some pictures as well, which are in his gallery here, IIRC. Maybe it'll be able to help you. Quote Link to comment Share on other sites More sharing options...
opcode Posted February 9, 2019 Share Posted February 9, 2019 That is right, check the LED datasheet. I believe blue LEDs usually use lower resistor values. Also keep anything that connects to Z80 pins as 5V. Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 Parkfun and I did some experiments with this a couple years ago.. He made a nice drawing of the pause mod w/sound off circuit and took some pictures as well, which are in his gallery here, IIRC. Maybe it'll be able to help you. Yeah, I know how to do the pause and sound mod, completed this on a CV a while back. What I want to do is to be able to add a pause LED but without changing the DPDT switch that I'm using. I'm absolutely certain that it's possible, just not sure exactly how just yet. Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 That is right, check the LED datasheet. I believe blue LEDs usually use lower resistor values. Also keep anything that connects to Z80 pins as 5V. Thanks - I'll check for the correct resistor value before I proceed to testing and will stick with +5V. Quote Link to comment Share on other sites More sharing options...
+grips03 Posted February 9, 2019 Share Posted February 9, 2019 add a Schottky diode 1 Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 add a Schottky diode Where and why? Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 This is my latest. I've added the existing +5V to BUSRQ via a 3.3K resistor for context, as well as showing the full DPDT switch with audio. The switch is shown with the system in normal operation (i.e. not paused). Thoughts? Quote Link to comment Share on other sites More sharing options...
+grips03 Posted February 9, 2019 Share Posted February 9, 2019 To prevent LED from always being on. Refer to schematic, post 3. Add Schottky diode, put anode towards Z80, cathode towards switch (same point as cathode of blue LED). Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 To prevent LED from always being on. Refer to schematic, post 3. Add Schottky diode, put anode towards Z80, cathode towards switch (same point as cathode of blue LED). Does the Schottky go in parallel or in series with the blue LED? Quote Link to comment Share on other sites More sharing options...
+grips03 Posted February 9, 2019 Share Posted February 9, 2019 Like this. I've not tested, but looks like it would work ok. Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 Like this. I've not tested, but looks like it would work ok. Great, thank you. I think I understand (almost anyway ). So, with the Shottky diode there am I right in thinking that now it shouldn't matter if I connect to the Z80 WAIT or the Z80 BUSRQ, i.e. if I connect to WAIT the Shottky diode will prevent the LED part of the circuit from affecting the WAIT line at the Z80? Quote Link to comment Share on other sites More sharing options...
+fdr4prez Posted February 9, 2019 Share Posted February 9, 2019 use a 3PDT switch if you want the LED circuit will be separate/isolated Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 use a 3PDT switch if you want the LED circuit will be separate/isolated Yes, I know that a 3PDT switch would separate things and would be ideal, but I have a specific DPDT switch I want to use and I know it can be achieved (but just not how - although looks like we might have a solution above thanks to grips03). Quote Link to comment Share on other sites More sharing options...
+grips03 Posted February 9, 2019 Share Posted February 9, 2019 Might need another 330 ohm resistor in there, between Z80 and and Shottky diode. Does Wait ever go high? Shottky diode is to make it so only GND (low) goes to Wait pin. Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 What Shottky should I buy? I'm assuming that I want as low a forward voltage as possible. Is this suitable? Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 Might need another 330 ohm resistor in there, between Z80 and and Shottky diode. Does Wait ever go high? Shottky diode is to make it so only GND (low) goes to Wait pin. Isn't Wait held high, i.e. inactive (it is tied to +5V via a 2.7K resistor)? Quote Link to comment Share on other sites More sharing options...
+grips03 Posted February 9, 2019 Share Posted February 9, 2019 I have to admit I've not looked at this enough. Perhaps something more is needed? If I have time I'll look at it more. Quote Link to comment Share on other sites More sharing options...
Ikrananka Posted February 9, 2019 Author Share Posted February 9, 2019 I have to admit I've not looked at this enough. Perhaps something more is needed? If I have time I'll look at it more. Thank you - I really appreciate your help Quote Link to comment Share on other sites More sharing options...
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