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4 Digit Presettable Down Counter Kit image Zoom

4 Digit Presettable Down Counter Kit

SKU: QK154
Four modes of presettable downcounting with reset and output. Uses a microcontroller to save all the work. Similar circuit to QK129 Up/Down Counter Kit. 9 - 12VDC.

Availability: In stock
Assembly Required: Yes

$21.95

SKU:QK154

Assembly Required!
Product Description

    Details

    NTRODUCTION This is a low cost 4 Digit Presettable Down Counter with output and reset. The count input can be used for both high and low speed counting applications. The counter has four modes of operation that control how the output behaves when the count reaches zero. The input, output and power supply pins are brought out to a 10-way header strip for easy connection. A 9 to 12V DC supply is required to power the kit, which has a current consumption of 20mA to 40mA, depending on the number displayed. A 12VDC / 150mA plug pack will do fine.

    4 Digit Presettable Down Counter Kit
    TECHNICAL SPECIFICATIONS

    Supply voltage 50mA @ 12VDC
    Operating modes Count Stop, Output Hold
    Over-Count, Output Hold
    Auto-Reset, One-Shot Output
    Over-Count, One-Shot Output
    Count range 0000 to 9999 (10,000 max)
    Count speed Low (selectable) High 30 cps (15mS high, 15mS low)
    30,000 cps (measured)
    Inputs Reset, Count, Rate
    Output Transistor, NPN, 100mA @ 30V
    Display 14mm RED LED
    Physical size 51mm x 63mm (2.0" x 2.5")
    Connection 10 pin SIL header pins, 0.1"
    INPUTS AND OUTPUTS

    These are organized as pairs of pins, with each input or output having a corresponding ground pin. Inputs are normally pulled high and may be driven low by simple "make" contacts from switches, relays or open collector outputs. There are three inputs:

    RESET Resets the counter to its preset value

    RATE
    Selects if debouncing is applied to the count input

    COUNT Triggers counter on falling edge

    The
    RATE input is used to enable or disable debouncing on the count input. With RATE high (open) debounce is enabled; with RATE low (closed) debounce is disabled. Enable debounce when using relay contacts or switches for input. The debounce time is 15mS for both falling and rising edges. This means the count input must be stable for at least 15mS before it is recognized, giving a maximum counting speed of about 30 counts per second. The open collector OUTPUT pin indicates when the count has reached zero. It needs an external pull-up resistor or it can be used to directly switch a relay. The OUTPUT is normally high and either pulses low or remains low depending on the operating mode. OUTPUT PULSE WIDTH (Mode C and D only) The OUTPUT goes low when the count reaches 0000. It stays low until the next valid count input when it goes high again. So, the OUTPUT pulse width depends on the speed of the count input. So, if the count input speed is 1000cps, the pulse width will be 1mS (1/speed). If the count input speed is 10cps the pulse width will be 100mS. OPERATING MODES There are four operating modes that control the operation of the counter and the output pin. The RESET input does not affect the operating mode. Mode A...........count stop, output hold (default) When the count reaches zero the output goes low and stays low. The counter stops counting. Reset to continue. This is the operating mode on power up. Mode B...........over-count, output hold When the count reaches zero the output goes low and stays low. The count will wrap around to 9999 on the next count input and continue counting from there. Mode C...........auto-reset, one-shot output When the count reaches zero, the counter automatically resets itself to the preset value and the output pulses low. The pulse width depends on the speed of the count input. Mode D...........over-count, one-shot output When the count reaches zero the output pulses low. The count will wrap around to 9999 on the next count input and continue counting from there. The output pulse width depends on the speed of the count input.

    PROGRAMMING THE COUNTER

    Two pushbutton switches, marked "SET" and "INC", are used to preset the starting count and select the operating mode. Presetting the count value is done one digit at a time, starting with the thousands digit. Press the SET button to enter programming mode. The display shows the current preset value of the thousands digit and the rest of the display shows minus (-) signs. Use the INC button to set the value required. Press the SET button when done. The current preset hundreds digit is shown. Use the INC button to set the value required. Press the SET button when done. Repeat the above steps for the tens and units digits. After setting the units digit the display shows the current operating mode. The mode is indicated by the letters "A, b, C or d". Use the INC button to set the operating mode then press SET to exit programming mode. The display will blank momentarily to indicate that programming mode has ended. The counter is now ready for use! As mentioned before the RESET input resets the counter to its preset value. It does not change the operating mode. If the counter loses power it will restart in Mode A with a preset value of "0000" (count = 10,000).

    CIRCUITᅠ DESCRIPTION

    The circuit used in this kit uses only one IC  the AT90S1200. It is one of the AVR family of RISC based microcontrollers from ATMEL. The pdf data sheet can be viewed (and downloaded) at "http://www.atmel.com" The IC is preprogrammed. Using a microcontroller greatly reduces the component count while providing more features than could be found using dedicated logic ICs. Cost is also lower. The AT90S1200 was the choice in this kit because it has an internal RC oscillator, eliminating the need for an external crystal and loading capacitors. The display is a single unit, common anode LED, MUX (multiplexed) display. This means that the anodes of every segment in a digit are connected together (internally) while the cathodes of like segments in each digit are tied to a common 7-segment bus line (A, B, C, etc). This minimizes the number of pins needed to drive the display but requires a more complex method to do it. Multiplexing is a technique where each display is "active" for a short period of time. In this kit, each digit is turned ON once every 8mS for a period of 1mS. There is an OFF time of 1mS between digits. Resistors R1-7 limit the maximum current that can flow through each segment. Transistors Q1-4 provide power to each digit. Each input to the IC is connected via an RC network. This RC network provides some protection against high frequency noise. For the values used the time constant is approx. 20uS. Shorter duration pulses will not get through. Transistor Q5 provides an active low, open collector overflow signal. Zener diode Z1 protects the transistor against high voltage spikes if used to drive a relay. The circuitry is powered by IC2, a 5V regulator. Diode D1 protects against polarity reversal on its input.ᅠᅠ

    ᅠᅠ

Additional Information

    Additional Information

    SKU QK154
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