Pause Mod LED

[Osgeld]

https://www.digikey.com/products/en/switches/rocker-switches/195?FV=2080004%2C3ac0001%2Cffe000c3%2Cc3c00e8%2Cc3c00ee%2Cc3c010c%2Cc3c0122%2Cc3c0048%2Cc3c0051&quantity=0&ColumnSort=1000011&page=1&stock=1&pageSize=25

[Ikrananka]

https://www.digikey.com/products/en/switches/rocker-switches/195?FV=2080004%2C3ac0001%2Cffe000c3%2Cc3c00e8%2Cc3c00ee%2Cc3c010c%2Cc3c0122%2Cc3c0048%2Cc3c0051&quantity=0&ColumnSort=1000011&page=1&stock=1&pageSize=25

 

Yep - that's exactly what I found before. The two switches I posted pictures of are both in that list. I've used similar searches on DigiKey, Mouser, RS Components, Element14, switch manufacturer websites and local suppliers with nothing better coming up.

 

Snap-in panel mount switches are problematic for two reasons, (i) the ColecoVision is 4mm thick which is too much for all of the snap-ins I looked at, and (ii) this then throws me back into looking for another way to mount my PCB.

 

I much prefer, in this case, a switch that has a circular threaded mounting using a nut to tighten. Easy to drill a hole, easy to install and will hold my PCB in place. The two switches I posted meet those criterion but I hate the 4mm thick bezel. In my opinion, these two switches will look ridiculous on a ColecoVision.

Edited February 17, 2019 by Ikrananka

[Ikrananka]

Well, a friend of mine would say "Use a knife switch." He loves the mad scientist look.

 

On a more serious note, perhaps an analog switch IC could be used as a relay, so that the switch itself doesn't have to do so much. For instance, an Intersil DG413 has 4 independent switches. 2 are normally closed, and 2 are normally open. So by hooking the same input to all the switch "actuator" pins, you have a functional DPDT relay. This would open up your switch choices to anything from SPST up. This particular chip claims to come in a PDIP package too.

 

Knife switches are cool, in a bringing Frankenstein to life kind of way

 

Anyway, looks like we had similar thoughts (although I'm a lot slower than you). I woke up early this morning and couldn't get back to sleep thinking about switches (how sad is that) and then the quad SPST HEF4066 that is in the ColecoVision sprung to mind. So, in a round about way I came to the same conclusion as you. Use a CMOS analog switch.

 

After some research this morning, I'm moving towards continuing to use my original Radio Shack (DPST) switch. One pole of this switch will handle the audio on/off while the other pole will be the +5V on/off signal to a SPDT (or dual SPST) CMOS switch. I'm currently favouring the MAX4544CPA+ which is an 8-pin DIP, seems to have good specs, and is cheap at ~$2 each. This switch will be the one that activates the system pause and LED blinking. I'll knock up a revised circuit diagram later today.

 

Am I right in thinking that CMOS analog switches will not work with momentary switching signals, i.e. the internal switches are not latching but will always revert to their "normal" position when the signal line drops low?

Edited February 17, 2019 by Ikrananka

[ChildOfCv]

 

Am I right in thinking that CMOS analog switches will not work with momentary switching signals, i.e. the internal switches are not latching but will always revert to their "normal" position when the signal line drops low?

 

Well, there might be a latching switch or two out there, but the one you're looking at does not latch. You'll need to use a pull-down resistor for when the switch disconnects though.

[Ikrananka]

Okay, here's an updated draft schematic with the MAX4544CPA analog switch included with an input signal pulldown resistor (R4). I do have some questions about this which I'll put at the end of this post.

 

 

Updated draft PCB images:

 

 

Questions

1. The MAX4544 has an max 60 ohm ON resistance. Will this be a problem pulling the Z80 BUSRQ low?
2. How do I calculate the value for the pull-down resistor? I understand that I need to know the MAX4544 IN leakage current but it doesn't seem to be specified in the datasheet.
3. With the current design I have the MAX4544 IN pulled high (+5V) during normal operation of the CV. IN is only pulled low when the system is paused. Is this okay or would it be better to have IN low during normal operation and only pulled high when the Z80 is paused. Or does it not really matter? I'm thinking about leakage past the pulldown resistor drawing unnecessary current. Is it best to minimise the duration of this? I am able to swap the IN high/low around by a manual rejig of the Radio Shack switch internals (which can be easily done if necessary).

Thanks

[ChildOfCv]

1) 60 ohms dividing the voltage with the 3.3K pull-up resistor will give you a 0.01V pull-down. That ought to be enough. Nobody else should be dumping amps into this part of the circuit--everybody on this line will only pull to ground. If you connect it to WAIT instead, that's still only 0.02V. Anything below 0.8 is a low.

 

2) 10K will work. So would 1M probably, and that will keep your leakage low. All you need for the resistor is for it to offer a little gravity.

 

3) Well, you don't really have a choice about how to wire the mechanical switch since "paused" has to be the same as "audio disconnected." For the analog switch, though, the IN is such a high resistance that you don't need to worry about whether it sees a high or a low most of the time. The IN itself measures leakage in nano-amps. And either way the chip will be connecting the common to one of the switching pins most of the time.

[Ikrananka]

Fantastic - thanks ChildOfCv for all your help with this - I'm nearly ready to order parts to prototype and test.

 

I did a little more reading this morning and realised that I could switch things around and change from a pull-down resistor configuration to a pull-up resistor configuration. So, in the latter case I take the +5V supply, put it through a pull-up resistor and tie that to IN on the analog switch. IN is also then fed to my Radio Shack Switch which now simply connects that line to GND when closed (which it would be in normal operation). The NO and NC lines are also swapped.

 

Is there any advantage to using one case over the other in this circuit?

 

Pull-Down

 

 

Pull-Up

 

[Ikrananka]

3) Well, you don't really have a choice about how to wire the mechanical switch since "paused" has to be the same as "audio disconnected."

 

The nice thing about the Radio Shack switch is that it can be easily changed internally so that instead of operating with both poles being ON or both poles OFF, it can be made to work with one pole ON and the other OFF and vice versa.

[+fdr4prez]

Instead of blinking, would be any easier to use a multi-color LED, so one color for ON and different color for pause?

[Osgeld]

or just use a blinking led hehe

[Ikrananka]

Instead of blinking, would be any easier to use a multi-color LED, so one color for ON and different color for pause?

 

 

or just use a blinking led hehe

 

I've already considered both of these options. I thought about using a multi-colour LED but decided that personally I much preferred the idea of the power LED slowly blinking while paused.

 

As I want to only have a single LED installed, an off the shelf blinking LED won't work as it always blinks and can't be made to stay lit continuously. I suspect that it was an off the shelf blinking LED that Yurkie used for his mod - but he then had a separate LED for power which isn't what I want.

[Ikrananka]

Made a number of minor tweaks to the design and have now ordered prototype PCBs and parts, including a custom 3D printed spacer/washer. Should have them all by mid March after which I'll do assembly, testing and possibly further tweaking. I'll post an update then and will also ask for a list of people who would be interested in buying this mod.

 

I plan on later making around 10 kits to sell for DIY install. This will include ALL parts, including the switch and wires, an installation guide and a drilling template. You'll need to be comfortable with drilling and soldering to complete this install.

Edited February 23, 2019 by Ikrananka

[Ikrananka]

I received the parts for the pause mod a few weeks ago but have only just now assembled everything to test it. I'm delighted to say that the flashing power/pause LED mod works exactly as expected. I need to make a few minor tweaks to the board dimensions, and a few other things, but I'd classify the prototype testing as a success. I'll post some pictures and a short video very soon.

 

One outstanding issue is around the audio side of things and specifically with regard to the SGM. When I switch to pause I want to be able to turn off audio not only from the CV onboard audio (SN76489) but also from the SGM if playing an SGM game.

 

Am I correct in thinking that SGM audio is fed to the CV via the expansion connector line 31 (EXAUD)? So, if I want to be able to switch both onboard (SN76489) and SGM audio on and off via a switch I would need to do the following, cut the trace AFTER C100 (red cross) as this is where both audio feeds come together?

 

 

Note that AUDIOOUT and EXAUD come together at the first leg of C100 and so it is not possible to cut a single trace before C100 and also means that any audio jack mod needs to be taken on the downstream side of C100 and not C88 as is often done.

 

Thoughts? Suggestions?

[Ikrananka]

Or if you're not using the CVs RF output (and don't care if audio to that isn't turned off when paused) and you have separate audio output jack(s) from a mod then this might be preferable.

 

 

This is certainly the case for me as I'm installing this on an F18A modded CV that has a separate audio output jack. So, I'll probably do mine this way.

 

The more I think about this the better this option is looking.

1. Any audio (SN76489 and SGM) to the audio jack will be turned off when the pause switch is engaged.
2. If you want to use an Exp. Mod #1 through RF then this still works as before regardless of position of the pause switch. This is technically the correct thing to do as the Exp. Mod #1 uses its own processor and pausing the CVs Z80 has no effect on it.
3. It avoids the need to cut any traces (I hate having to cut traces unless absolutely necessary).

[Ikrananka]

As promised, here are some pictures of the assembly process for the flashing LED pause mod, the finished installation and also a video of the mod in action. I'll be putting these into some proper instructions at a later date along with a drilling template for the holes in the case.

Holes Drilled

Assembled Prototype PCB

Note that the LED and resistor value are exactly the same as that used in the SGM (thanks Opcode) and so has exactly the same look and intensity. They complement one another perfectly.

Also note that I had originally planned on soldering the input wires to the board but changed my mind during assembly as this would mean that you'd have to desolder the wires to remove the board if needed. So, I grabbed a temporary 4 pin connector out of my spares to use with a Molex connector (see the photo of the assembled wire assembly below). I'll be using a proper white locking Molex four pin connector on future PCBs.

Wire Assembly

Pause Switch Installed

This also has the 3D printed custom spacer installed. This keeps the PCB just very slightly above the surrounding case plastic and also provides a solid base beneath the PCB against which the threaded switch nut screws down against.

PCB Installed

Note that I had to sand down a lot of the teeth on the nut that screws down the switch and holds everything in place. Without doing this there just wasn't enough thread available/visible on the switch for the nut to get a grip. The sanded nut gets a nice good grip on the threads and tightens down nicely. In the picture below the nut on the left has been sanded while the one on the right is untouched.

Motherboard Wiring Assembly

Motherboard Installed

Mating Up Mod Connectors

The Mod in Action

https://youtu.be/3gLRwBwKslc

[Ikrananka]

What do you think of the flashing frequency? Is it too slow or just right?

 

It can be easily adjusted during PCB assembly by changing the value of two resistors on the PCB. I kind of like the lazy slow flashing I have set as this makes it much less distracting than with it flashing rapidly. But I'm curious to know what you think.

 

If I do sell this mod as a kit then I could tailor the supplied resistors to the flashing frequency that you prefer.

[Ikrananka]

Also, huge thanks to @ChildOfCv for his suggestions and troubleshooting tips during development of the schematic for this mod, without which I wouldn't have been able to do this.

 

THANKS ChildOfCv

[Tursi]

That's pretty cool!

 

The blink seems slow to me, but what about just using a trimmer pot there so it's adjustable?

[Ikrananka]

That's pretty cool!

 

The blink seems slow to me, but what about just using a trimmer pot there so it's adjustable?

 

I agree - after using this for a little while I too am inclined to feel that it is flashing a little too slowly.

 

I like your suggestion of using a trimmer pot and so have now added this to the design. I've designed this to allow the flashing to be varied from 0.6 Hz (roughly what it is in my current prototype) to 3.0 Hz which I feel is likely the fastest anyone would want. It took a little time to squeeze the trimmer in (top left) and to make the other tweaks that I needed to do. The board is now 0.4mm narrower so that it fits perfectly in the CV and I have also added the Molex 4 pin connector. Here's the current PCB layout which I'll likely order as a prototype again just to make sure everything is okay before offering to others.

 

[Ikrananka]

Finally found time to finish off this mod and am now offering complete kits for sale here:

 

 

[doubledown]

Fancy kit...looks good.

 

I'll stick with my plug-n-play version:  ?

 

 

Assuming of course an SGM isn't plugged in.

 

Seriously looks good, just found this pic and had to post.

[Ikrananka]

15 hours ago, doubledown said:

Fancy kit...looks good.

 

I'll stick with my plug-n-play version:  ?

 

Assuming of course an SGM isn't plugged in.

 

Seriously looks good, just found this pic and had to post.

Thanks ?

 

I remember when you got hold of that unit.  Very nice find and one I've never seen anywhere else since.  Shame the LED doesn't flash ?

[doubledown]

Remember flashing lights cause seizures and I won't be a party to that.  You should include a notice with your kit like Nintendo does for your own legal protection.

 

Besides, who needs flashing, unless in your case, the LED is also a power indicator, then yes flashing is necessary.  

 

I just opted for separate power and pause lights:

 

 

[Ikrananka]

Ah but my recommended frequency range (1 to 2 Hz) is that used for vehicle signals and they don't come with legal notices.  Besides, my YouTube video allows someone to test if they'll get seizures before purchase by simply watching the video (just in case anyone thinks I'm being serious let me clarify - I'm not).

 

 

[doubledown]

I see your lawyers advised you well!