DT205 Relay Board on a SimmStickTM Bus

Control External devices from a SimmStick micro or your PC Parallel Printer Port.

Features

• Boards are cascadable so that 16 relays could be run with 4 boards.
• Status LEDs across each relay coil.
• Relay & LED supply can be 5 - 12 Volts.
• Uses a single ULN2803 or ULN2003 to select a group of 4 bus signals out of 16.
• Used with the DT004 board, a stand alone Printer Port to Relay board is produced, no Microcontroller!

View Schematic

DT205 Bare Board (as supplied)

The DT205 is a 2.5 Inch Board so it's marginally more expensive than the 2" boards.

Overview

The board design allows a wide range of relays to be used. Designing for just one type would have yielded a smaller board, the increase in flexibility more than makes up for the increased size (it's 2.65" long, so it's called it a 2.5" board).

It uses a single ULN2803 or ULN2003 to select a group of 4 bus signals out of 16, namely D0 to D15. If you use a ULN2003, make sure it plugs into the correct spot on the socket. This is bottom justified, leaving pins 1 and 18 of the socket blank.

The AUX VBB/GND input terminals appear to be in an awkward spot but in practice, this isn't a problem. When using the DT205 in a Simm socket, you connect up the power before inserting it. If it connects via male/female pins, it isn't a problem anyway.

Four LEDs and resistors across the coils enable the relay state to be monitored. 560 Ohm resistors have been chosen so that 5 to 12 Volts can be readily used on the LEDs and coils.

For testing, a 3 pin header is provided so that VBB can be easily jumpered to either +5V or PWR signals on the SimmStick Bus.

Parts List

1 x DT205 PCB
1 x ULN2803 or ULN2003 Driver Chip
1 x 18 pin socket. (Optional)
8 x 9 pin strips of socket header pins.(Optional)
4 x 560 Ohm Resistors .25 watt
4 x 5mm LEDs.
2 x 6 way PCB mount Screw terminals .2 Inch centers.
1 x 2 way PCB mount Screw terminal .2 Inch centers.
A set of 3 male header pins and a test or shorting shunt. (Optional).
4 suitable Relays. Read text below.

NOTE *** If your DT205 is only going to be set for a group of 4 signals then you can solder your chip straight into the board, or at least use a single socket.

Assembly

Not that difficult, but I would recommend using the 8 socket strips for the chip if this is the first you have put this board together.

If it is for development, it would pay you to get the 8 strips of socket pins so that any group of 4 signals can be selected.

Control Signals

The ULN2003/2803 select one four bit set of control signals from D0-3,D4-7, D8-11 and D12-15. This is done by installing the chip into one of four different positions on the board:

• D0-D3,      use E1     

• D4 to D7,   use E2     

• D8 to D11,  use E3     

• D12 to D15, use E4     

 

ULN2003/ULN2803 Differences

The only difference beween the two chips is the extra gate and two extra pins at one end of the chip, so either chip can be used as only 4 gates are connected to the Relays. Just make sure that you bottom justify the chip to line up with the ground and VBB pins.

If using D0 to D3 to drive the four Relays, install your ULN2803 into the E1 pin 1 position. This is shown on the overlay as '1' and lines up with '8'. The 8 signifies that you are using an 8 bit driver chip. If you were to use a 7 bit ULN2003 driver I.C., then pin 1 lines up with '1' and '7'. This will leave pins 1 and 18 blank on the socket.

All hand assembly should be done by installing the shortest height components first.
Resistors don't matter as the legs can be bent over to hold these in place at any time.

Suggested Assembly Order

1. Install the Socket or socket header pins.
2. Install the 4 LEDs. The Cathode end is nearest the SimmStick bus. It is shown on the overlay as the dark flat marking near the lower leg. The LED itself has one leg shorter than the other. This is the cathode. It also has a flat edge. This also marks the cathode.
3. Install the 1 by 3 pin header block for the test or shorting link.
4. Install all Resistors standing upright with one leg bend over the body of the resistor so that each one will fit the .1" pattern as shown on the overlay of the board..
5. Install the 3 sets of screw terminals.
6. You can install your Relays after you have tested the LED operation of the board if you wish.
7. Then insert your chip. You are finished.

Testing

The walking LED test program sample is all you need to make this board work.

Alternate Supply Voltages

The 560 Ohm resistor has been chosen so that it can be used with both +5V and approx. 12 to 15 Volts. Power can be supplied to the board from one of 3 sources.

1. On J3, connect your shorting link on the 3 pin header between +5V and VBB. This is enough to turn on the LEDs, however the voltage probably won't be enough to pull in the Relays.
2. Connect the shorting link between VBB and PWR on J3. This should make the Relays operate.
3. For serious Relay work, an alternative power supply may be needed. If multiple boards are used, the existing SimmStick power supply may well fall short on being able to provide enough power if Relays are being switched on at once. The VBB/GND screw terminals are used for this function. Don't install a test link on J3 if using the AUX VBB input.

Cascading Boards

The DT205 Relay board can be plugged straight into a SimmStick bus via a Simm Socket, or it could be mated with a main-board or motherboard using right angle male and female pins. If the later is done, you can then solder a right angle female connector to the board so that additional Relay boards can be added.

NOTE ****
Only the SimmStick bus signals D4 to D15, plus PWR, +5V, and ground are allowed to continue on the bus, so if you are using D0 to D3 for Relays, then this board must be the first in the chain.

Modification - Track Missing

It's only a minor fault, and will only be noticed if you are cascading boards. The D5 input doesn't connect to the J4 D5 ouput. The missing track can be easily seen on the solder side of the board.

Relay Selection
Here are the measurement in inches of the relay base dimensions for the DT205 Relay board.
There are 9 large 50 mil holes on 100mil pads. The dimensions are shown below. All other holes are 35mil in 62 mil pads. These are all at 0.1 inch centres in a grid pattern.

The relay coil can be at .1", .2", .3", or .475" centres. The row of holes below the relay coil are at the .1" pattern. The lower large hole is used for the common connection relay contact on some relay types.

TOP VIEW:

Relay Types
As more International universal Relay types become known, the list will be updated.
The Digi-Key Z271-ND is the same base as the Good Sky Relay.