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Visual Basic

Using VB With IASI2

Source code for this can be found in the downloads section.

This is a screen shot of a VB program written in VB 2005 Express Edition that will directly interface to an IASI2 device either connected to a COM port or through a converter device such as a BV101 or BV201

Here is a BV4102 Matrix connected to a BV101

Connecting to the PC

Method 1 By direct connection to a COM port or through a serial connector. All IASI2 devices can be connected directly to a COM port or through a USB to serial converter, Prolific for example. The wiring diagram is shown here:

A practical set up, the white lead has 4 wires and comes from the COM port. The plus 5V is provided by a BV1102 which is wired into the connector. Shown is the back of an IASI2 LCD display.

A power supply will be needed (see bv1102) as the COM power does not provide any power of its own, unlike the newer USB specification. This is called the inverted method because the output from RS232 is inverted. All IASI2 devices default to inverted at start up.

Method 2 By using a serial to TTL, Logic convertor. This method is the same as that used for direct connection to a microcontroller but as we are using a PC, the RS232 signals will need to be converted to 5V levels.

Option A - MAX232

The MAX232 is a buffer driver chip that will convert the voltage levels used in RS232 (+ and - 12V) to 5V logic levels, for convenience the BV201 is available that uses the MAX232 but also has the 9 pin connector required for connection directly to a RS232 COM port.

This shows a practical example connecting a BV4103 to a RS232 COM port via the MAX232 (BV201) converter, this time the power supply is required to power both the BV210 and the BV4103.

Option B USB

There are a few USB-TTL converter on the market, these should not be confused with the Prolific type that convert USB to RS232. ByVac has one called the BV101.

This shows that a BV101 can connect directly to an IASI device.

This option is probably the easiest as the connection can be done directly and there is no need for a power supply. Pin 4 is not connected to anything on the BV101 and so can either be connected or not. A convenient method of connecting several devices together is to use a 10 way ribbon cable and IDC connectors as no soldering will be required.

Only half of the 10 way cable is used and only one side of the 10 way connector, this is because it is not possible to get a 5 way IDC connector but for convenience there is nothing to beat it especially when connecting multiple IASI devices on the same bus.

The Software

IASI-Generic

All IASI devices work on simple text commands so it is a matter for the software to send the appropriate text via a COM port. To illustrate this as simply as possible download the IASI-Generic source code from the software section. The code has two VB files, one for the form and the other dedicated to IASI. The following describes how the software works in sections so that you can use or modify it according to your project. This code has been made as simple as possible to illustarte the concepts when using these devices.

Opening the COM Port

This is a vital step as all communication will be via the COM port. When the form opens it runs Populate_Ports(). This conveniently gathers all of the available ports on the system and places them in the combo box. Opening the COM port with cmdOpen_Click enables the rest of the form panels and turns the button green. Any errors at this point will be trapped by the system as error checking has been purposely left out to make the code simpler to understand and use.

Establishing a Connection

There are two options for establishing a connection, RS232 and UART. The RS232 is for when the device is connected directly to the PC COM port and is called INVERTED and UART for when the device is connected via method 2 described above and is called non-inverted.

A connection is established by sending 2 or 3 bytes with a value of 13 (ASCII Carriage Return - CR) followed by a byte with a value of 1. For non-inverted connections another byte is required with a value of 4. This can actually be sent before or after the '1' command. This is taken care of by Connect subroutine in the IASI.VB module. On successful connection the device will return its address followed by '>'. Each device has its own time slot for responding to command 1, address 'a' will respond first and address 'z' last. It can take up to 800 ms for 'z' to respond and hence the delay.

For working systems this routine could be improved by checking for the correct response and re-trying if required. For this program all that happens is the returned result is displayed in the text box opposite the button.

Sending Commands

A command is placed in the text box including the address and will be sent when the button is pressed, the result will be displayed in the edit box at the bottom of the form.

The Prompt

Most commands when successfully completed by the device will send back a prompt this is a byte with the value of 62 (0x3e) which is the ASCII code for '>'. Application software can take advantage of this. In the function SendText a command is sent to the device via the COM port (Form1.Sout('command')) and then a loop is set up that will exit when '>' is received. Just in case there is a problem with the device or the command a timer is used that will cause the loop to exit.

For a more complex example look at the other VB code in the software list.