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I found this parking meter at Princess Auto yesterday. Made by POM Inc., this meter is called the PPM.

I got it to work by adding a rubber band with just enough tension to depress the turn-detect lever when the lever is turned. The meter has knobs where a tensioned spring was attached. I’ll have to find a decent spring somewhere.

Opening it up, I found that the coin detector uses a series of armatures and four switches to detect which coin was inserted.

Upon examination, it has 6 buttons:

• (Top Left) Yellow button for debug output
• (Bottom Left) Yellow button for turn-sense
• White buttons (4) for coin sense

When a Quarter is inserted into the proper slot and the arm is turned…

1. As the coin lever is turned, the turn button is pressed.
2. As it passes the buttons, the quarter makes the arm hit all 4 white buttons, in a clockwise order starting with the top left.
3. When the turn lever is released, it returns to its original position, and releases the turn button.

When a Dime is inserted into the proper slot and the arm is turned…

1. As the coin lever is turned, the turn button is pressed.
2. As it passes the buttons in a clockwise order starting with the top left, the quarter makes the arm skip the first white button, and hits the remaining 3 white buttons.
3. When the turn lever is released, it returns to its original position, and releases the turn button.

When a Nickel is inserted into the proper slot and the arm is turned…

1. As the coin lever is turned, the turn button is pressed.
2. As it passes the buttons in a clockwise order starting with the top left, the quarter makes the arm skip the first 2 white buttons, and hits the remaining 2 white buttons.
3. When the turn lever is released, it returns to its original position, and releases the turn button.

When you press the Debug button, the front LCD shows the following:

1. Test pattern: “c2:2c”, where the last ‘c’ is backwards.
2. Firmware Version?: “0159”, also the number writen on a sticker on top of the ST27C256
3. Parking Limit: “0002”, maximum number of hours allowed to park
4. Route?: “0321”, also printed on a sticker on the back of the meter. This was the same for other meters i saw.
5. Unknown: “8:5”, “8:6”

Interesting innards:

LCD/LEDs

• LCD1: LCD, Front: 4-digit, “88:88” LCD
• LCD, Back: Red, Clear background. No text.
• D3: Red LED, (clear casing)
• D4: IR LED
• D5: IR Sensor

Switches

• SW5,6: Yellow Switches (Surface mount)
• SW1,2,3,4: White Switches (Surface mount)

ICs

• U6: Motorola MC14519B – Four bit AND/OR selector
• U2: Motorola MC14521B –
• U7: Motorola MC145453FN – LCD 33-Segment LCD Driver, Serial, CMOS
• U5: Motorola MC68HC11A1FN – Motorola 8-bit Microcontroller, 256 Kbit RAM, A/D converter, EEPROM
• U4: Fairchild MM74HC373WM

  – 3-STATE Octal D-Type Latch

• U3: THMOS ST27C256 – 256Kbit (32Kx8) CMOS 3-STATE (UV-Erasable?) EPROM
• U1: 271BC – Programmable Low-Power OP-Amp
• U8: Motorola HC20 – Dual 4-input NAND gate
• U9: 74HC02M – Quad 2-Input NOR Gate
  

Headers

• J2: 4-pin header
• JP4, JP3, JP2, JP1: Jumpers, unpopulated, to ground certain pins on U5

See also:
http://www.globalnerdy.com/2008/07/17/rubyfringe-guide-active-surplus-aka-hardware-nerdvana/
Pics in action:
http://www.sonomatlc.org/Parking/PBDs/Pkg_Benefit_Districts.htm
http://www.dkimages.com/discover/DKIMAGES/Discover/Home/Geography/North-America/United-States/Travellers-Needs/Practical-Information/Transportation/Roads/Chicago/Parking-Meter/Parking-Meter-1.html