My challenge here is with limited electronics understanding; the picaxe aspect is quite straightforward.
The objective is a 12V DC switch that stays on for a short time (order of 3 minutes) then switches off, completely disconnecting the timer circuit as well as the load. It's a light switch on a sailing boat; the light is in an obscure locker and leaving the light on could go unnoticed for a long time, dangerous for the battery. The timer circuit must also be disconnected completely when not in use to protect the battery.
I have attached an outline circuit that I thought would work.
View attachment Delay Switch concept.pdf
Pressing the momentary switch powers the 5V regulator for the Picaxe which has a very simple program:
This latches power to the picaxe and the load for the required time, then switches the load and the picaxe off at the MOSFET.
The trouble is, the off switching doesn't work. Using a 2N7000 or STP36NF06L, the gate voltage doesn't fall low enough to switch off. Is this a fundamental flaw of the design or is the concept sound but with a problem in the detail?
I have found a module on ebay that can achieve my initial objective but I'd like to understand what is wrong with this idea.
Derek
The objective is a 12V DC switch that stays on for a short time (order of 3 minutes) then switches off, completely disconnecting the timer circuit as well as the load. It's a light switch on a sailing boat; the light is in an obscure locker and leaving the light on could go unnoticed for a long time, dangerous for the battery. The timer circuit must also be disconnected completely when not in use to protect the battery.
I have attached an outline circuit that I thought would work.
View attachment Delay Switch concept.pdf
Pressing the momentary switch powers the 5V regulator for the Picaxe which has a very simple program:
Code:
high 2
pause 3 minutes
low 2
The trouble is, the off switching doesn't work. Using a 2N7000 or STP36NF06L, the gate voltage doesn't fall low enough to switch off. Is this a fundamental flaw of the design or is the concept sound but with a problem in the detail?
I have found a module on ebay that can achieve my initial objective but I'd like to understand what is wrong with this idea.
Derek