Serial Wombat
a general-purpose digital interface device for hobbyists, engineers and students

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Getting Started with your Serial Wombat

There are three major steps which need to be accomplished to control your Serial Wombat with a PC:

• Build your 5 volt power supply circuit
• Build your RS232 to TTL voltage converter
• Connecting power and serial communications to your Serial Wombat

Note: Many of the videos below require a data rate higher than some users can support. I recommend right-clicking and doing a "Save target as..." to save the video to your hard drive before watching.

If you haven't used a breadboard before, watch this video.

Step 1: Build your 5 volt power supply circuit

Your Serial Wombat requires a regulated 5 volt power supply to function. If you already have an off-the-shelf regulated 5 volt supply, skip to step 2. The instructions below assume you have purchased a Serial Wombat Starter Kit, and have a 9-volt battery, and a multi-meter. A "Wall Wart" transformer may be substituted for a battery.

The Serial Wombat Starter Kit includes a LM7805CT voltage regulator (datasheet) which will provide 5v, +/- 4% at up to 1 amp. This regulator is very cheap, easy to use, and hard to kill. However, it is not very power efficient (it wastes about 7ma regardless of how much power your circuit draws), has a high drop-out voltage (the voltage above the desired voltage which must be provided as an input) of 2 volts (meaning you have to supply at least 7 volts input), and doesn't respond as quickly to load changes as many other regulators. Some users will find the LM7805CT an adequate choice, and use it for their projects. Others will use the LM7805CT as an easy way to get started, then change later to a regulator which fits their specific needs.

Building your 5 Volt supply is easy! Just follow these steps:

1. Use your voltage meter to test your battery. If it's less than 9 volts, buy a new one, because this one doesn't have much life left (9-volts are convenient and compact, but don't have much capacity).
2. Attach the 9-volt connector to the battery, and verify that the voltage is present on the ends of the wire leads using your MultiMeter.
3. Plug your LM7805CT into your breadboard. One side of the LM7805CT is mostly metal. Turn your breadboard so the mostly metal side is facing you.
4. Disconnect the 9-volt connector from the battery.
5. Plug the red wire from the 9-volt connector into the breadboard in the same row as the rightmost pin of the LM7805CT.
6. Plug the black wire from the 9-volt connector into the breadboard in the same row as the center pin of the LM7805CT. This pin will serve as the ground for the rest of the system.
7. Attach your multi-meter black (or ground) test lead to the top metal piece of the LM7805CT. This piece of metal is connected to the center pin, which is the ground for your circuit.
8. Attach your multi-meter red (or positive) test lead to the leftmost pin on the LM7805CT. Set the mult-meter to measure volts.
9. Momentarily connect the 9-volt battery to the battery connector. Your meter should read 5 volts while the battery is connected. If not, recheck your connections and fix any problems before going forward.
10. Attach one of the capacitors from the Wombat Starter Kit to the left and center pins of the LM7805CT. This will slightly improve the response of the regulator to changes in load, and make your circuits more stable.
11. On each side of your breadboard there are two long rows (called rails). Select one rail on each side for positive voltage, and one rail on each side for ground. Some breadboards will already have these marked. If not, I suggest using a red magic marker to draw a red line over the rail you choose to be positive. Connect the leftmost pin of the LM7805CT to the positive rails, and the center pin of the LM7805CT to the ground rails.
12. Some breadboards split their side rails in half. In order to get power and ground to the far ends of these breadboards, wire jumpers must be used to bridge the two halves. Check if your breadboard needs jumpers by inserting wires in the rails as far from your LM7805CT. Connect your 9-volt battery, and see if you can measure 5 volts between your power and ground rails. If not, add jumpers to bridge the two halves of the breadboard.
13. Disconnect your 9-volt battery.
14. Connect the longer wire from one of the red LEDs from your Wombat Starter kit to a +5 power rail near your regulator. Connect the other end to an unused row in your breadboard. DO NOT CONNECT THE LED TO POWER AND GROUND WITHOUT USING A RESISTOR! You will burn out the LED.
15. Connect one of the 220 Ohm (Red-Red-Brown-Gold) resistors to the row connected to the LED. Connect the other end of the resistor to the ground rail.
16. Momentarily connect the 9-volt battery to its connector. The LED should light. Mentally note how bright it is.

Step 2: Build your RS-232 to Logic Level converter circuit

1. Solder wires to your DB-9 connector.  The Serial Wombat uses a three-wire serial connection.  The wires should be soldered to pins 2, 3, and 5.  Pins 2 and 3 are signal lines, and 5 is ground.  If your DB-9 is female, then the top rightmost pin (as you look at the solder-side of the DB-9) is pin 5.  The second from the left is pin 2, and the middle is pin 3.  If your DB-9 is male, then the top leftmost pin (as you look at the solder-side of the DB-9) is pin 5.  The second from the right is pin 2, and the middle is pin 3.  (Most DB-9s also have the pin numbers molded in the plastic in really-small, hard to see numbers).  At this point, we won't say which signal pin is receive and which is transmit, as this can vary depending on what you're plugging your Serial Wombat into (A PC, a Palm Pilot Cradle, a modem, etc, although this set of instructions assumes you're using a PC), and how any intermediate serial cables are wired.  

2. Open Windows Hyperterminal from the Accessories...Communications menu in Windows.  Choose "File...Properties".  Choose your COM port (often COM1), and press the Configure Button.  Set

9600 Bits-Per-Second,
8 data bits
Parity: None
1 Stop Bit
Flow control: None

Choose OK and exit the menus.  If you wish, you may save this configuration for later use with the File...'Save As' option.   

3. Press the 'Call' button (the telephone).  If you get a message which says "Unable to open COM1" then some other program is probably using the COM port.  Shut down any programs such as those which sync to a Palm or Pocket PC and try again.  

4. Type a few characters in the terminal.  You should not see any characters on the screen, since what you type is being sent out the PC's serial port, and nothing is connected.  If you see your characters (or any others), then you either have the wrong COM port, or local echo is enabled for your port (turn this off under "File..Properties..Setting...Ascii Setup".  

5. Connect the two signal wires of your DB9 connector to each other, then plug the connector into your PC's serial port.  Don't connect ground to anything for now.  Start typing in Hyperterminal.  You should see what you typed appear in the terminal screen.  This is called a "Loop Back Test".  What you typed is sent out of the PC's serial port on the transmit line, and looped right back in on the receive line (since they are connected).  If you don't see your characters appear on the screen when you type them, then something is wrong.  Check the following:

• Flow control should be turned off in the Hyperterminal Configuration of your COM port. 
  
• Verify that your wires are soldered correctly to the DB-9.  There should be wires on pins 2,3, and 5.  Male connectors and female connectors are soldered differently.  Connect your multi-meter between the signal wires and the ground wire while the DB-9 is connected to the PC.  You should see a voltage equal to or greater than 5 volts, or a voltage equal to or more negative than -5 volts.  There are multiple pins on the PC's COM port with these voltages;  Detecting a voltage doesn't necessarily mean that everything's OK, but no voltage means there's a problem.

6. Unplug the DB-9 from the PC.  Disconnect the signal lines from each other.  Plug the DB-9 back in and type some characters in hyperterminal.  You shouldn't see any, since the loop is broken.  If you see characters, then your signal pins may have been bridged together when you soldered the wires to the DB-9.  Remove the DB-9 from the PC and use your multimeter to check to see if pins 2 and 3 are bridged.  

7. With the DB-9 plugged into the PC and the signal wires disconnected, check both signal wires against ground to see which has a voltage which is either greater than +5 volts, or more negative than -5 volts.  The signal wire with this voltage present is the PC's transmit line, and the Serial Wombat's Receive Line.  From this point forward, the signal wires will be described from the Serial Wombat's point of view.  Therefore, the line with a voltage on it will be called the "Receive line" from here forward.  The other signal line will be called the "Transmit Line".  (If both wires have voltage, then guess which one is RX.  If, in step 12 you fail the loop-back test, then guess the opposite, and try again).  

8. The Serial Wombat expects logic-level (0 to 5 volt) inputs. But RS-232 can range as wide as plus and minus 12 volts. The ADM202EANZ (datasheet) provided in your starter kit converts these voltages in both the transmit and receive directions. In this step you build the ADM202EANZ circuit (all pin numbers in this step refer to pins on the ADM202EANZ):

• Disable power to your circuit
  
• Connect ground to pin 15
  
• Connect +5 volts to pin 16
  
• Connect a capacitor between pin 1 and pin 3.  Polarized capacitors should have + on pin 1.
  
• Connect a capacitor between pin 4 and pin 5.  Polarized capacitors should have + on pin 4.
  
• Connect a capacitor between pin 16 and ground.  Polarized capacitors should have + on pin 16.
  
• Connect a capacitor between pin 16 and pin 2.  Polaraized capacitors should have + on pin 2.
  
• Connect a capacitor between pin 6 and ground.  Polarized capacitors should have + on ground, since pin 6 will have a negative voltage when energized.

9. Double check your connections.  

10. Apply power to your circuit.  The ADM202EANZ should not draw more than 10ma current from the +5 volt supply.  If you are using the 7805 regulator and power status LED included with the Starter Kit, then apply power momentarily and observe the LED.  The LED brightness should be as bright as before the creation of the ADM202EANZ circuit.  If the LED is visibly dimmer, then something is wrong.  Disconnect power immediatly and recheck your circuit.  

11. Use a voltage meter to measure the voltage on pin 2.  It should be +8 volts or higher.  Use a voltage meter to measure the voltage on pin 6.  It should be -8 volts or less (i.e. more negative).  

12. Test the functionality of your circuit.

• Disconnect power to your circuit. 
  
• Connect the ground wire from your DB-9 to the ground of the ADM202EANZ circuit. 
  
• Connect the Receive line from the DB-9 to pin 8 of the ADM202EANZ. 
  
• Connect the Transmit line from the DB-9 to pin 7 of the ADM202EANZ. 
  
• Connect pin 9 of the ADM202EANZ to pin 10 of the ADM202EANZ. 
• This will create a loop-back through the ADM202EANZ chip.  Connect the DB-9 to the PC.  Apply power to your circuit.  Type a few characters in Hyperterminal.  They should be echoed back.  If not, recheck your connections.  After sucessfully verifying the Loopback echo in hyperterminal, remove the wire connecting pins 9 and 10.

Step 3: Wire up your Serial Wombat

1. Connect Wombat pins 12 and 31 to ground

2. Connect Wombat pins 11 and 32 to +5 volts

3. Place connect Wombat pins 11 and 12 with a capacitor

4. Place connect Wombat pins 31 and 32 with a capacitor

5. Connect pin 10 on the ADM202EANZ to pin 25 (TX) on the Wombat

6. Connect pin 9 on the ADM202EANZ to pin 26 (RX) on the Wombat

7. Connect a 10k (Brown-Black-Orange-Gold) resistor to +5 Volts and pin 1 (MCLR) on the Wombat

8. Connect a 10k (Brown-Black-Orange-Gold) resistor to +5 Volts and pin 6 (boot) on the Wombat

Test your Serial Wombat

1. Connect your serial cable to your computer.

2. Open Hyperterminal as described above.

3. Power your circuit

4. Type "U" 10 times to set your baud rate and synchronize the Wombat. (Press shift and U 10 times, don't type the quotes). Nothing should appear on hyperterminal.

5. Type "!1234567" (Don't type the quotes). Your message should be echoed by the Wombat back to hyperterminal.

6. Disconnect power from your circuit.

7. Connect the long end of an LED to +5 volts. Connect a 220 ohm (red-red-brown-gold) resistor to the short end of the LED and to Wombat pin 19.

8. Power your circuit.

9. Type "U" 10 times to set your baud rate and synchronize the Wombat.

10. Type "P190<space><space><space><space>" this will set Pin 19 low, allowing current to flow through the LED and into the Wombat. The LED should be lit.

11. Type "P19I<space><space><space><space>" this will set Pin 19 to input, a high resistance state which will stop current from flowing through the LED.