Dear all,
I have the Picaxe 18 Project board (CHI030) with all inputs modified for digital use. The ULN driver IC is fed by 20V and the Picaxe 18 by 5V from a 78L05 also fed by the 20V by a series resistor of 470R. The level of the input signals is 20V so a voltage divider is created by 33k resistors in series with the on-board 10k resistors. The length of the wires to the input signals are about 2m long. The state of the inputs is +20V or floating but, the input pins of the picaxe are grounded by the on-board 10k resistors. The function of the picaxe in this is that three inputs (0, 1 or 2) are read (button command) and after some seconds a pulse is generated (pulsout command) on the corresponding outputs 0, 1 or 2. This works but, at unpredictable times, when the input lines are floating the picaxe generates pulses on the outputs as if there were input pulses. Then I put relays on the input to make the floating input grounded but the problem remains. Only when moving the relays near to the picaxe the problem has gone: the length of a wire from a relay to the picaxe is about 15 cm, the input states are +20V (+5V on picaxe input) or ground and the long (+20V or floating) wire switches a relay.
Is there a maximum length known of digital input lines to have the picaxe operate without failing?
Thanks in advance,
Herman, NL
I have the Picaxe 18 Project board (CHI030) with all inputs modified for digital use. The ULN driver IC is fed by 20V and the Picaxe 18 by 5V from a 78L05 also fed by the 20V by a series resistor of 470R. The level of the input signals is 20V so a voltage divider is created by 33k resistors in series with the on-board 10k resistors. The length of the wires to the input signals are about 2m long. The state of the inputs is +20V or floating but, the input pins of the picaxe are grounded by the on-board 10k resistors. The function of the picaxe in this is that three inputs (0, 1 or 2) are read (button command) and after some seconds a pulse is generated (pulsout command) on the corresponding outputs 0, 1 or 2. This works but, at unpredictable times, when the input lines are floating the picaxe generates pulses on the outputs as if there were input pulses. Then I put relays on the input to make the floating input grounded but the problem remains. Only when moving the relays near to the picaxe the problem has gone: the length of a wire from a relay to the picaxe is about 15 cm, the input states are +20V (+5V on picaxe input) or ground and the long (+20V or floating) wire switches a relay.
Is there a maximum length known of digital input lines to have the picaxe operate without failing?
Thanks in advance,
Herman, NL