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(RSS) Automatic device detector

IP.com Disclosure Number: IPCOM000031473D
Original Publication Date: 2004-Sep-27
Included in the Prior Art Database: 2004-Sep-27
Document File: 2 page(s) / 31K

Publishing Venue



Determines supply voltage required by a cash drawer based on load characteristics of the cash drawer. Current solutions typically require additional signals in the connector that define the device type. This disclosure describes a scheme that works with existing hardware and does not require additional signals in the connector.

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(RSS) Automatic device detector

Automatic device detection

      IBM has 2 types of cash drawers that have been made available on past POS system lines. One drawer type is powered off of+24VDC and the other drawer type is powered off of +38VDC. Our new generation of POS terminals has to be able to allow for the connection of either type of drawer, using the same connector, even though the operating voltages of the drawers are different.

     An automatic cash drawer voltage selector circuit has been developed that will automatically detect the voltage required to drive the cash drawer and apply it to the system connector(s). This circuit works automatically at power on. No jumpers or other manual settings must be made to appropriately set the correct voltage.

A block diagram of the circuit is shown below:

    Each cash drawer has a certain default resistive load characteristic that is unique to the device. The difference in load can be determined by measuring the current consumption of the device at a known voltage. By measuring this current and comparing to known values, a decision can be made that will identify the type of cash drawer attached, and define what actions need to be taken.

    In the current implementation, the current is measured when power is first applied. The power supply provides a signal that defines when all power supply voltages are stable (power good). At power good time, the circuit measures the amount of current being provided, and then makes a decision an...