In Progress Mishmash Homebrew - Pt II - Playable Coffee Table

[Ashbo]

Quick update - having a few days with normal life usually helps and this time it's no different. I have been reading up around how the ESP32 works and it seems I have been setting my tasks (which I pin to cores) with too high a priority. The more I pin at a high priority the less stable the ESP32 will become. There are many internal processes that need to take place to keep the system on a chip running and if I am too agressive with my code it all breaks down. This is what I saw with my LED corruption. I have since made a table of what's running on each core so I can visualise what is going on and this helps me to ensure higher priority tasks keep running (Pinball stuff) and lower priority tasks need to wait (Web server).



So first test this morning and no LED corruption. I'll likely have some undesirable impact on the pinball game (always a sceptic) but at least I can start to plan how I will manage to prioritise resources on this awesome little chip.

 

[Ashbo]

A day of highs and lows. High point was getting some functions set up to do a basic chase, all on all off and odds and evens given an array of LEDs

The low was plugging my dev board into the wrong sockets and mincing it with. That's another £6.99 wasted

 

[Ashbo]

Picked up an old oak TV table that I plan to repurpose/salvage the wood from to make the surround .... May need to see if I can get some help from my dad (as is the way )

 

[Ashbo]

Plucked up the courage to assemble and test the power filter board. (OPP Project - https://pinballmakers.com/wiki/index.php?title=OPP#Hardware)



The theory here is the bulk capacitors will hold enough charge to fire coils without stressing the 48v switched power supply.

It was very scary firing this up for the first time. One thing wrong and that's potentially an expensive repair bill.

As it happens it went to plan, however I need to change where this sits in the design as currently it's wired up after the 48v relay I have, this means it can provide its residual capacity to coils even after the relay is deactivated. Not ideal. I also need to find some way of safely discharging the caps as they have a dangerous level of charge in storage when off.

 

[Ashbo]

I've been relying on my favourite (and only ) dad to help with (do all of) the work in cutting down the oak TV stand so it will become the coffee table top for this project.



Some interesting structural features to navigate, but I have been assured all will be well

 

[Ashbo]

Rewired the 48v so the power filter board sits between the 48v rail and the PSU the PSU goes to fuse, then relay, the power filter then a feed to 48v rail and a feed to the play field coils. This stops coils firing on startup when the relay is off.

We do still store 48v in the caps on power off, I need to put in a bleeder resistor. This could be a 5W 10k resistor across the caps, but it's more likely a 10ohm 20W resistor across the caps but switched on only when the power is off.

I have been playing with creating some tunes on the chimes and testing flippers. The EOS switch on the upper right flipper is a bit old and will need a replacement . This wasnt working as expected so adjusted when I checked the coil as it was getting a bit hot.

A bit of a visual of the flippers. It's nice the PSU isn't cutting out now.

 

[lukewells]

We do still store 48v in the caps on power off, I need to put in a bleeder resistor. This could be a 5W 10k resistor across the caps, but it's more likely a 10ohm 20W resistor across the caps but switched on only when the power is off.

A 10ohm resistor would be seeing 230watts being dissipated across it, so don't do that

A 10k 1/2watt resistor in parallel with the capacitor would be fine (the actual power is about a quarter watt at 10k) You could also add a power LED in parallel as well, so you will have a visual indication of the charge state as well as speeding the discharge slightly

 

[Ashbo]

A 10ohm resistor would be seeing 230watts being dissipated across it, so don't do that

A 10k 1/2watt resistor in parallel with the capacitor would be fine (the actual power is about a quarter watt at 10k) You could also add a power LED in parallel as well, so you will have a visual indication of the charge state as well as speeding the discharge slightly

Nice one @lukewells. I think I'll give that a go, assume a suitable resistor in front of the led to prevent further destruction

 

[lukewells]

Nice one @lukewells. I think I'll give that a go, assume a suitable resistor in front of the led to prevent further destruction

A 4.7k resistor would give you 10ma into an average red led, but it would be dissipating near 1/2 watt

I would suggest you can improve the situation by using a blue LED as they tend to have a higher forward voltage, so will put less strain on your resistor. a 1watt would be better, but a 1/2watt is probably fine.

Also now that I calculated the power at the resistor, the LED and its resistor would actually run down the caps in a reasonable time alone. Adding a second dedicated bleed resistor in parallel would not be strictly required, but hey resistors are cheap and it would just make it faster.

Hope that made sense? (so 4.7k res + LED in series, placed parallel to the caps, then optionally another 10k resistor (also in parallel to the caps))

 

[Ashbo]

A 4.7k resistor would give you 10ma into an average red led, but it would be dissipating near 1/2 watt

I would suggest you can improve the situation by using a blue LED as they tend to have a higher forward voltage, so will put less strain on your resistor. a 1watt would be better, but a 1/2watt is probably fine.

Also now that I calculated the power at the resistor, the LED and its resistor would actually run down the caps in a reasonable time alone. Adding a second dedicated bleed resistor in parallel would not be strictly required, but hey resistors are cheap and it would just make it faster.

Hope that made sense? (so 4.7k res + LED in series, placed parallel to the caps, then optionally another 10k resistor (also in parallel to the caps))

Perfect sense sir. Thanks for the explanation. I think this may be achievable onboard the opp circuit board, but will do it parallel from the outputs ( I have one pair spare) top and bottom right most on the output connector. Top positive and bottom ground.

 

[Ashbo]

A monumental effort from my brilliant dad means I can now order some glass...






...it was a tough job with steel fillets reinforcing the original mitre joints. These needed to be removed and hardwood fillets being used once cut down. The side strips were also never level and corners that were once legs were cut down, glued and screwed.

Not a bad result for a £20 upcycle project.

The glass (10mm thick toughened glass with beveled and polished edges) will be considerably more expensive.

 

[Ashbo]

Added some Rust-Oleum Chalk Finish Furniture paint and some brass corners.





Also, after reusing the old glass with some sticky rubber pads, I think I may hold off ordering the new glass ..