Thursday, June 17, 2010

Built-In Self-Diagnostics for Your Next Invention

If your invention involves the use of a microprocessor then there is an opportunity to employ self-diagnostics in your new invention.

What is self-diagnostics? I think of it as the ability of a product to communicate to the user when something goes wrong and to provide strong clues about what it is that is malfunctioning.

A while back I invented a hot water delivery system that pumps the hot water from your water heater to your fixtures at high speed without running water down the drain and only when you actually want hot water.

The invention utilized a Microchip brand microprocessor chip to control the pump. When you want hot water you push a button which tells the pump to begin pumping. The pump mounts under the sink where you want the hot water. The pump has a built in temperature sensor that tells the microprocessor when the hot water arrives and the microprocessor then turns off the pump.

If the water in the pump is already hot then the pump will not start when the button is pushed. This is a safety feature to prevent scalding in case someone is in the shower and someone else comes along and pushes the button without realizing there is already hot water or that someone else is in the shower. This is necessary because the pump can be controlled from more than one location since often more than one fixture benefits from the pump. The number of fixtures affected depends upon your plumbing layout.

Another safety feature built into the system times the run time of the pump, and if the pump runs for over 3 minutes the circuit shuts the pump off. This is in case of a water heater failure. If no hot water arrives the pump will just keep running. This feature prevents that from happening.

Adding in Self Diagnostics Capability to the Invention

I took advantage of the power of these little microprocessor chips in several ways to build diagnostic capabilities into my new invention. They are simple, but seeing as they don’t require additional hardware or circuitry they are well worth the effort.

The first feature I added was to let the operator know that there was already hot water at the fixture when they pushed the button. Without such a feature the pump simply would not start. At that point the operator does not know hot water is already there and may simply thing the pump is not working. It’s quite likely the operator or homeowner will stand there and push the button several more times trying to get it to work. This makes for a frustrated customer.

What I did was to have the pump pulse on for ½ second twice, separated by a ½ second wait. When the home owner pushes the button and the pump pulses on twice, he knows the water at the pump is already hot and he can go ahead and use the fixture.

Another feature we added was to have the pump check for a short circuit on the control wires for the start button. Frequently customers will use X10 remote controls to operate the hot water pump. Sometimes the X10 controller, a UM506 remote receiver, can lock up in the on position which would cause the pump to behave in undesirable ways.

What I did was to have the microprocessor chip monitor the control wires. To start the pump the button needs to be pressed and then released. Upon releasing the button the pump starts up. But if the chip does not detect a release within 15 seconds it begins pulsing for ½ second every 15 seconds which tells the home owner there is a short on the control wires.

This feature has saved us a lot of grief and money. Without this feature the invention would end up being returned for warranty service and create unhappy customers. Now they know to check the button or the UM506 if this behavior occurs. If they email or call complaining the unit doesn’t work and the symptoms they describe match the self diagnostic behaviors built into the pump we can advise them quickly what the problem and solutions are.

It was certainly well worth the effort.

You can see the invention here: Chilipepper Hot Water Demand System