Cable Problem


New Member

I have recently made a simple sensor light for the garage, operated by a picaxe 18A on a CHI 030 high power protoboard. The 12volt PIR detector power is connected to one of the FETs to save power so that I can program it only to run at night. Light levels are sensed by an L.D.R.
The protoboard has obviously had the resistor cut as to run the FETs off 12volt. The picaxe is running on 5volt through a voltage regulator, as the main power source is a 12volt battery.
Light is provided by a 12volt 50watt halogen light controlled by a relay.
...Thats the technical specs
The problem I have had is, once programmed , with my laptop still plugged in (on site with all lights etc plugged into the protoboard) The light works fine (switches on when I walk in front of it etc) However when I unplug my computer the program stops working...
The picaxe seems to run without the computer plugged in on more simple programs but just not the most recent one. It seems like it needs to be plugged it when using the L.D.R? As the other programs I have tested not using the L.D.R seem to work.
Does anyone know what effect the computer could be having on the circuit? I am not sure what the next step is as I know the program works, as it runs fine when my computer is plugged in?
Thanks very much for your help.


Sounds like this is one for the enhanced download circuit.
At a guess, you have an LDR as part of a potential divider and the resistive part of the divider is a high value.
When the download cable is connected there can be a small negative voltage applied to the PICAXE serial input. This can upset the ADC reading when the total resistance 'seen' by the ADC input is above about 10k.

You will either need to use the enhanced download circuit to re-calibrate your cut-off value or use some form of display (eg AXE033) to show the ADC value when the cable is not connected. It would also be possible to calculate the ADC value by measuring the voltage at the ADC pin.


Senior Member
Just a thought...

Did you leave the programming resistors in your circuit? I haven't had any problems with the 18x but I have with 28x1's and 08's. The programming pin shouldn't be left floating and needs the 10k / 22k resistors or it can pic up static and end up locked "high" and in programing mode.