arduino Switch transistor with a low voltage and current


Posted on Feb 6, 2014

Designing a circuit that will use a combination of switches and resistors to allow a microcontroller to identify which switch was pressed based on the voltage read and perform a switch-specific action. The design that I`ve come up with involves using a transistor to activate a relay, which powers the microcontroller. When the microcontroller is powered, it pulls a pin high to take over powering the relay. When the action is finished


arduino Switch transistor with a low voltage and current
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the microcontroller pulls the pin low, deactivating the relay and cutting power to the microcontroller. I`ve tested the circuit with one switch and a voltage divider to simulate the largest resistor/lowest voltage combination from my switch array. The voltage that I`ve calculated at the transistor is 1. 6 V, and the current is 0. 017 mA. The high resistor values are necessary since I need approximately 0. 2 V differential between switches. The problem is that the transistor is not being activated (it works if I feed it 5V directly). My question: Is this because the current is too low How would I go about rectifying this (other than decreasing resistances) If there is a better approach to this problem, I`d love to hear it also. This is a circuit for a picture frame that will do specific actions depending on the button that is pressed. This will be battery-operated using 6 D-cell batteries, mounted on the wall. I`d like to get months if not years of operation out of it before having to replace the unit. My Arduino with an attached shield (with using a MAX667 power supply rather than the stock one) consumes 45 mA at low power. The stock Arduino doesn`t go into low power mode although with a programmer the chip can be modified to go into low power mode and consume nA of current. At 45 mA, the batteries will last about 11 days (266 hours for a 12000 mAh battery). Hence the requirement that the resistive ladder turn on the...




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