Appendix A: QScreen Electrical Specifications

The QScreen Controller combines an embedded computer based on the 68HC11 microcontroller with a touch panel and LCD (liquid crystal display) graphic user interface (GUI) that is ideal for instrument control and automation.

Motorola 68HC11F1 microcontroller with 16 MHz clock speed and 4 MHz bus speed. Paged memory expands the processor’s address space to 8 Megabytes.

3 or 4 input capture functions facilitate accurate detection of pulse edges and measurement of pulse widths with a resolution of 2μs.

4 or 5 output compare functions make it easy to create complex waveforms and pulse-width modulated signals up to 20KHz at 50% CPU load.

A pulse accumulator facilitates frequency measurement and pulse counting up to 2MHz.

21 interrupts support the 68HC11’s on-chip subsystems.

A watchdog timer and clock monitor ensures orderly reset after an error.

High contrast CCFL white-on-blue monochrome LCD display with software controlled backlight.

4.8" diagonal (4.25" x 2.25"), 240 x 128 pixel display.

5 column by 4 row touchscreen with software controlled beeper for audible feedback. Custom antiglare, clear, and EMI touchscreens are also available for quantity orders.

Optional intrinsic safety barrier on touchscreen.

A hardware UART supports either RS232 or RS485 at up to 19.2 Kbaud.

A second software UART implements RS232 at up to 4800 baud.

A fast synchronous serial peripheral interface (SPI) provides communications at speeds up to 2 megabaud.

Your QScreen includes a high-efficiency switching regulator with surge suppression, transient filtering, and EMI/RFI filtering to provide clean supplies for the onboard analog and digital electronics. You need only supply regulated or unregulated DC power in the range of 8 to 26 volts.

Surge Suppression

The raw input is protected by a "varistor" rated at 33 Volts DC. This metal oxide surge suppresser protects a Qscreen by clamping high voltage spikes before they have a chance to do any harm. The varistor has no effect if the input voltage is less than the maximum specified, or 26 volts. Above 33 volts the device starts to conduct current, and it acts like a short circuit to high voltages, thus clamping the voltage spikes. To prevent this varistor from consuming current, you should make sure that the maximum DC voltage supplied is always less than 26 volts.

EMI/RFI filter

Additional protection is provided by an electro-magnetic interference (EMI) and radio frequency interference (RFI) filter that prevents high frequency noise from invading the circuitry via the power input, and also prevents EMI from propagating back to the external power supply. The EMI filter is implemented by a two stage PI network of inductors and capacitors. The output of the first stage filter, called V+raw, is passed to the Wildcard module bus for supply to Wildcard modules that require their own unregulated DC power. This unregulated voltage is free of high-frequency and high-voltage transients. If you design custom add-on Wildcard boards, we recommend that you use V+raw as the input for local 5 Volt regulators. It is good design practice to place local voltage regulators on each board, as this minimizes noise problems and improves modularity.

The QScreen Controller is designed for reliable low noise operation. It is implemented as a state of the art 6-layer surface-mount board. Two inner layers are dedicated ground and power planes, providing low-impedance return paths for digital current spikes.