FreePlay 555 Coin Circuit

My Sega Star Trek Captain’s Chair is destined to be present at the 2012 Texas Pinball Festival. As a result; the game needs to have a FreePlay feature (IE a way for the public to play the game without needing quarters). I know Sega Star Trek has a freeplay rom hack available; however, at this moment, VectorLabs isn’t supplying freeplay roms with their devices. I haven’t spent enough time with the multi-vector boardset to determine how easy/hard it would be to convert to Freeplay. As a result; I wanted a simple inexpensive way to credit up the machine when the user pressed the Start button (1UP).

I toyed with the idea of using a cheap 8pin ATMEL microcontroller; but decided a simple 555 timer could be developed to do most of the heavy lifting. In the end I decided to go with a dual 555 timer (NE556) in a cascaded mono-stable configuration. The circuit features:

  • PowerOn Reset to “credit up” a single credit when power is applied to the machine. Jumpered feature.
  • Ability to drive COIN_NO signals
  • Ability to “interrupt” COIN_NC
  • Can be alternatively stuffed for AC power supplies (6.3VAC GI circuits in Pinball Coindoors).
  • Jumper configuration to “disable” circuit.
  • Barrier Diodes to help prevent “installation error”.

I have decided to release this design under to the public under the TAPR Non-Commercial Open Hardware License which indicates:

You may make products based upon this design, provided you do not make more than ten units in any twelve month period for your personal use.

Schematics :

Click to view FreePlay 555 Schematics in PDF

The first timer conditions the active low switch connected to J2-3 (1P [aka the start button]). On the Sega vector hardware; this signal is tied high to 5V via a 2.2K pullup resistor. The start button connects momentary grounds at this signal. The Trigger on the 555 timer is also triggered when the voltage at pin 6 transitions below 1/3VCC. D4 protects the cpu board by preventing current from flowing back into the cpu board. This timer “de-bounces” the switch which sends a single long pulse via OUT1 (pin 5). This timing is created by TA = C6*R4 or ~242mS. I’ll explain the function of R5, JP3, D1, and C7 later.

OUT1 drives the “armed” LED to notify the user/debugger that a “start” pulse was received. OUT1 is coupled to Timer2 via C4 and R6. The purpose of these components is to provide a “negative” trigger pulse at the falling edge of Output. Timer2 then drives based upon TB = R1*C1 or ~60mS. This is the coinup signal which is sent to the coin circuit of the arcade machine. 60mS was derived from measurements of my acutal Star Trek Captain’s Chair by dropping a quarter into the slot via an Oscope.

OUT2 (pin9) drives Q2 and Q1 respectively. When not processing “start/coin up signals” Q1 is “active” providing conduction between the CPU Board and the Switch (PNP active when base is low). On the sega star trek; I found that I had to interrupt the NC signal of the switch in the coin door to get the cpu to “detect” a coin from our COIN_NO (J2-4) – Q1 provides this interruption. Speaking of NO, Q2 goes active when OUT2 outputs a high… which drives a “low” to the COIN_NO. In the Vector machine; COIN_NO is pulled high thru another 2.2k resistor and drives the !Set signal of a Set/Reset Latch made out of NAND gates. Incidentally; the NC signal drives the !Reset signal. The Q output of the NAND gate drives the clock of a D latch which drives the interrupt pin to the cpu board.

I promised to talk about the R5/C7 combo. These components control the “poweron” coin up timing. TpwrCoin is a function of U2’s timing and R5*C7 which is basically ~1.2seconds. U2 is a ActiveLow microprocessor supervisor IC. It monitors the 5V powersupply and holds !RST low for about 150mS. This allows the top of R5 high thru a 5.5k internal pullup resistor when the device is non-active. Meaning U2 will drive RST high on each timer after 150ms once the 5V rail is at least within 15% of the 5V target (4.25V). This effectively provides a “credit” signal to the game about 1.2seconds after the power button is pressed (for initial credits). In theory; this circuit can be disabled by removing JP3’s shunt.

JP1 provides a mechanism to “disable” the freeplay circuit. IE virtually removing the circuit from your game. Use this in position [2-3] to disconnect the timers from the bases of the transistors which should return the game to normal operation. IE if you want to start charging people money. I plan to use it to enable money when I take it for charity work.

Please be aware; this circuit still allows the coin shutes to work… even if the circuit is enabled. This was intentional.

The PCB is designed as a two layer PCB with through-hole parts on the top layer to enable those less skilled with a soldering iron to build the circuit.


FreePlay 555 Fab A Top Layer w/ Silkscreen


FreePlay 555 Fab A Bottom w/ Silkscreen

For those without PCB layout tools; a bare PCB is available from the batchpcb service for under $14. You can purchase the boards from this link:
http://batchpcb.com/index.php/Products/75967

The Bill Of Materials (BOM) of the board is available from Digikey for $9.02 (as of the time of this post). A bom is included with the schematics PDF above, but An XLS file with the digikey part numbers with the complete package of the materials above as a single download: FreePlay555_pkg

The author’s prototype was built from mostly RadioShack parts he had in his parts bin including the breadboard. He intends to replace this with a PCB from batchpcb in a few months.

Installation note: You need to make sure this circuit used the same voltage rail of your cpu board. The authors’ G08 wiring harnesses did not follow either the Cockpit (which is correct) schematics or the Upright harness (which is incorrect). The J4/P5/p12 harness¬† shows that the cockpit connects the coindoor lamps to the +5V rail at P5 pin6 and pin8. However, The author’s harness had it connected to the -5V rail which is BAD and will prevent the circuit from working properly (and possibly damaging your machine). The upright schematic shows that +5 and -5V goes to the lamps for 10V… also bad.
Either wire up a new +5V signal to this board; or correct your wiring harness to be like the schematics of the cockpit. Seriously – go double check it.

I wired in this circuit into the coin door harness so the board can be bolted to the inside the door. You’ll need to “cut” the NC wire of one of your coin switchs and put this circuit between it at J2-5 and J2-6. Then wire in the NO signal at J2-4. The Start Button goes to J2-3, the +5V rail to J2-1, and Ground to J2-2.

The circuit works as expected in my machine…. providing an inital “Free” credit upon powerup and then providing additional credits each time the start button is pressed (after the game starts). If you want more than one credit; the circuit can be redesigned; or you can press start multiple times during your “inital” game. ūüėČ

I’m fairly sure this circuit can be adapted to any arcade machine. I provided a bridge rectifier stuffing option at B1 to enable “AC” voltage inputs from 6.3V AC.¬† Or Jp2 can be “bridged” with solder to enable 5V to via the D3 shottkey diode.¬† I plan to test this circuit on my Bally Star Trek Pin once I get the PCBs back.

Enjoy… I’ll post more pictures when I get the PCBs back from batchpcb.

Star Trek HAPP CoinDoor Red Alert Indicator

On my Sega Star Trek Captain’s Chair restoration; I had to install a HAPP Coin Door¬†because I’ve been unable to¬†locate an original door. This Restoration is featured at¬†AustinModders.com¬†or KLOV.com for those that are interested in the complete project. Anyway, while installing my custom Coin Door inserts; I decided I wanted to modify the stock HAPP coin “guides”. The stock guides look to be black ABS and well … just don’t do it for me. The stock guides are shown here:

you can see the tiny little square just above the coin slot. This is the area we are going to target with this modification. Once you take apart the coin door; you’ll see guide is a piece of formed black abs:

Once I had this guide out; I measured it using a pair of Digital Calipers and layed it out in Corel Draw X4:

The “nubs” would be laser cut out of 1/8″ Red transparent Acrylic and the blanks would be cut out of black opaque acrylic.

The top of the red “nub” was sandblasted to give it a frosted looks so it’d defuse the light as it exits the nub. When assembled the new guide looks like this:

A 1206 Red LED was soldered into the red acrylic’s pocket with red rework wire attached to the anode and black to the cathode.

I need to drill the coin chute to¬†route the LED’s wires:

and I route the wires out the top side of the chute:

Now that I have the LEDs wired in… what am I going to use them for? Well; I decided I wanted to run the LEDs simular to the¬†Series’ Red Alert indictors I viewed a couple of youtube videos and did some wiki searches; but couldn’t find a “factoid” which gave me the timing of a TOS Red Alert indicator. Therefore; I just decided to make timing which would be pleasing to my eye. If anyone knows for sure a flash target; let me know or leave comment and I’ll figure out the correct timing circuit to flash at that rate.

Anyway; I decided to go with a somewhat simple 555 timer circuit. I have decided to release this  design under to the public under the TAPR Non-Commercial Open Hardware License which indicates:

You may make products based upon this design, provided you do not make more than ten units in any twelve month period for your personal use.

The 555 timer operates in Astable mode governed by R1,R2, and C1.

Schematics :


Click to view Red Alert Indicator Schematics in PDF

¬†The current implementation of the circuit has an “on” time of ~2.6 seconds and an off time of ~1/3 of a second. There is a RC timer made up of R3 and C2 which allows the LED to “wink” into it’s on state. LEDs D1 and D2 are driven by the 2N3904 transistor and wink on at the same time… Rather than do a current mirror; I decided to let D2’s current ~= D1s current given the transistor’s common-base current gain… IE alpha = beta/(beta+1)¬† which¬†@ ~20mA the 3904’s beta is a minimum of ~90… so alpha is .989 the current of D1. The circuit uses the RST pin of the 555Timer to add additional stability by putting a reset delay on the flipflop in the 555 at ~5seconds. Overkill; proably – but should be very reliable.

The current in the LEDs is controlled by R9 a series resistor intending to limit the current. It was emperically derived using SPICE as a starting point… and then the circuit breadboarded to maximize to 18mA of current flow. D4 is a schottky diode to protect the 555 from reverse wiring mistakes. The LEDs were left unprotected because they and the¬†BJT¬†are diodes … so shouldn’t be impacted by reverse wiring mistakes; additionally, the LEDs voltage drop is already ~2V.. so¬†the 0.1-0.3V voltage drop of D4¬†might effect brightness.

The PCB is designed as a two layer PCB with through-hole parts on the top layer to enable those less skilled with a soldering iron to build the circuit.


Red Alert LED Fab B Top Layer w/ Silkscreen


Red Alert LED Bottom w/ Silkscreen

 
For those without PCB layout tools; a bare PCB is available from the batchpcb service for under $11. You can purchase the boards from this link:
http://batchpcb.com/index.php/Products/68503

The Bill Of Materials (BOM) of the board is available from Digikey for under $6 (as of the time of this post). A CSV file with the digikey part numbers is here: HappLEDWink_r2.bom.csv

Here’s a package of the materials above as a single download: HAPPBlink_pkg.zip

Here is the the prototype assembled:

Next I needed to mount the PCB inside the coindoor. Since this is a modern replacement HAPP door; I decided to drill and put some #6-32 hex standoffs inside the door. I taped the holes and also added some epoxy to keep the standoffs in place:

I mounted the PCB:

The rework wire is self adhesive; which made it easy to route the led wires back to the PCB and secure it to the reverse-side of the coindoor.

Last but not least; I connected the power to the +5V circuit at the base of the 555 lamp on the coindoor. the lamp circuit on the Sega Star Trek is tied to the +5V PSU… it isn’t 6.3VAC like Pinball Machines.

Here’s the circuit installed and running:

Want to see it in action? Check out our YouTube video: