This is a follow on to a previous thread about the MC14490 debouncer IC.
My project has three components: an Arduino that only provides 3.3 V and ground to my breadboard; a breadboard with a circuit containing an SPST button and an MC14490 debouncer IC; and a GPS unit with an interrupt pin.
The MC14490 circuit appears to be working as expected. A probe on the output pin shows a nice solid low when the button is pressed. A volt meter across Vcc and the output pin shows zero normally, and 3.3 V when the button is pressed.
The interrupt pin on the GPS has an internal pullup. The interrupt works successfully with no debouncing IC. If I ground the interrupt pin anywhere (on the GPS PCB, or on the breadboard) it fires. The interrupt has 3.0 V across it. However when I connect it to the output pin on the MC14490 and press the button nothing happens.
What would be the explanation for that? The specifications seem to be OK: the MC14490 has a typical current on the output pins of -2.2 and 4.0 mA. The GPS has a maximum rating of 10 mA. Why does the low on the MC14490 not drive the interrupt low?
The GPS interrupt pin is not well documented. It is intended for Automotive Dead Reckoning, with input from a gyro or wheel tick. A diagram shows this input as a rising edge, although the internal pullup and the function of the pin suggest that it is in fact a falling edge.
My project has three components: an Arduino that only provides 3.3 V and ground to my breadboard; a breadboard with a circuit containing an SPST button and an MC14490 debouncer IC; and a GPS unit with an interrupt pin.
The MC14490 circuit appears to be working as expected. A probe on the output pin shows a nice solid low when the button is pressed. A volt meter across Vcc and the output pin shows zero normally, and 3.3 V when the button is pressed.
The interrupt pin on the GPS has an internal pullup. The interrupt works successfully with no debouncing IC. If I ground the interrupt pin anywhere (on the GPS PCB, or on the breadboard) it fires. The interrupt has 3.0 V across it. However when I connect it to the output pin on the MC14490 and press the button nothing happens.
What would be the explanation for that? The specifications seem to be OK: the MC14490 has a typical current on the output pins of -2.2 and 4.0 mA. The GPS has a maximum rating of 10 mA. Why does the low on the MC14490 not drive the interrupt low?
The GPS interrupt pin is not well documented. It is intended for Automotive Dead Reckoning, with input from a gyro or wheel tick. A diagram shows this input as a rising edge, although the internal pullup and the function of the pin suggest that it is in fact a falling edge.