Preface, operating principles

When working with microcontrollers, I often have to transfer data using UART interface on a microcontroller. Also RS232 interface, which basically extinct on nowadays laptop computers is still a golden standard with industrial electronics, so I have desinged simple interface, which may convert UART and RS232 signals to USB port. It can also be used as RS232-UART interface, if we want to connect microcontroller with some RS232 device such as GSM modem etc.

Operating modes

• As USB-UART interface (i.e. between microcontroller and computer)
• As USB-RS232 interface (i.e. between GSM modem (with RS232 interface, such as MC35i) and computer)
• As UART-RS232 interface (i.e. between GSM modem (with RS232 interface) and microcontroller)

Regarding to my positive experiences with FTDI chipsets (and as well some negative experiences with some china brand USB-TTL) I decided to use FTDI’s USB-TTL converter chip RS232RL, which I’ve used in many applications so far without problems. It requires minimal number of external components, is very stable and offers support for basically all operating systems.
As also conversion between TTL levels to RS232 is required. This means that logical levels on a processor (i.e. 0/5V or 0/3.3V) is changed to symetrical signal with higher voltages (+/- 12V) to avoid noise in a line. MAX232 can be used for this purposes, when using 5V TTL levels (for 3.3 and 5 V levels please use MAX323). The MAX chip only requires few external capacitors and it’s ready to work.

As often (especially in developing) we can power the device from USB port, I also added 4th pin, where +5V from USB connector can be routed (with connecting the jumper)

Building instructions
The circuit mainly contains SMD parts. We start with both chips, then mini USB connector, after that other components (resistors, capacitors, LED diodes – mind the polarity!).

Priklop in delovanje

When the circuit is soldered, we first check the resistance between GND and +5V, to make sure we do not have any short circuit, which could damage USB port. IF everything is ok, we connect the module to PC using USB mini cable. If the operating system doesn’t install the drivers automatically, we can get them at official FTDI web page (www.ftdichip.com).
There are 2 versions of drivers avalible: VCP (virtual com port), where our interface is displayed as virtual COM port and D2XX (direct), where direct access to the device is possible using DLL libraries. This option is useful, when we are making also own PC software, otherwise I usually use VCP drivers.

Some remarks

• Optional 10k (R1) resistor on ID pin of the USB connector

Some devices define, which device is A (ID pin to GND) or B (ID pin floating). Some other devices use this pin to define the required current for a device. 3 standard resistor valves are usually used between ID pin and GND:124k ohm, 68k in 36,5k ohm (see more at http://en.wikipedia.org/wiki/USB_On-The-Go)

• Jumper for power source selection

If we want to power the device through USB interface, add the jumper on the jumper headers. This way, +5V power supply is delievered to 4th pin on ghe UART and RS232 interface.

• Sigal diode between FTDI and MAX chip

MAX232 TX holds the TX line high (logical 1), which means that this line will not work properly. A small signal diode is added to seperate the TX line.

We often come into situation, where simple battery protection circuit is required.

Attached circuit id really simple, but very accurate and with extreme low power confumption ((4.5 uA!). With slight modifications, we can define shutdown voltage as well as voltage hysteresis.

We would also like to mention here, that we suggest setting a voltage treshold high enough (at least 3,0 V for LiIon/LiPo – or even higher), because this can improve battery lifetime significantly. With this, we loose some capacity, but not much really..

Article LT1389 (.pdf) - source: Linear Technologies

EN_1.0_ALTERUS – Users Manual

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EN_1.0_ALTERUS – Technical Manual

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SI_1.0_ALTERUS – Navodila za uporabo

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SI_1.0_ALTERUS – Tehnična navodila

The company base stays in Škofja Loka, however clients are welcome to visit us in Trzin!

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Parts of  the vehicle’s control systems were also developed by our company eCAT. Module teleCONN enables remote data reading and collecting, where display informs driver about current power consumption and other electric parameters of the vehicle.

• Link Metron
• More about (SLO)
• Official page (EN)
• Link 1
• Link 2
• Link 3

ALTERUS is really easy to operate and ensures data storing on cheap and avalible memory media (SD card). This solves the big problem of the current controllers (static memory media), where several organ players may re-write stored combinations of another organ player. Operating the system is very easy due to the graphic display and only some buttons with one-meaning-only (no need to learn button combinations etc.). This means, that even an older organ player, never seen a controller before, will be able to operate ALTERUS within a minute!

More about the controller is avalible on ALTERUS web page. (webpage is still in construction)

All captured data is send via Bluetooth interface to the smartphone for real-time overview as well as data is stored on internal micro SD memory card for further analisys.

The module is very simple to operate and – even more important – to integrate on basically any e-vehicle.

More info on catCAPTURE site!

We would like to thank you for cooperating with eCAT and wish you Mery Christmas and lots of success in the incoming year 2013.

eCAT team

More on: http://www.foruminovacij.si/index.php?t=newsSFI&id=1135

Presentation video: