Circuit Design Help

Technical Electrical
1

NOTE: No, this isn’t for the first competition. It’s for an exhibition which I hope to present at the National Science Bowl this year.

Anyway, I think all of our computers today have this special feature: Push the button to turn on the computer permanently.

A momentary switch (the button) somehow rearranges the circuit on the motherboard to turn on and keep on the computer. How does this work and can I incorporate it onto my circuit?

This circuit will be part of a fuel-cell powered car where the car will be mounted in its charging base at one end, and I will be at the other end, at least 10 meters away with the starting button/device. All I need to do is to push the momentary switch which will start the car and release it from the charging base.

The car is now under its own power from the fuel cell and speeding along the track to me.

Prior to starting, the car is plugged into a series of ac adapter-like plugs, which–when the car starts–are disconnected from the car as the car moves away from its base.

Any thoughts?

2

Actually to computer is already getting power (mother board) from the power supply that has a rocker switch on it. The button sends a signal to the mobo which then powers up the whole computer. I dont know how to make the circuit like you want but you could do the rocker switch with a push button.

You can use a memory logic cuircut to do what you want.

3

Computer power systems work in different ways, depending on how old it is, what type it is, etc. In the old days the switch was on the power supply, it was an on/off switch that disconnected the AC power cord wiring from the rest of the power supply. Modern PCs have a power supply designed to always provide a standby power source to the motherboard, and when this is connected to another pin on the power supply, it tells the power supply to “turn on”, and provide power to all the other outputs.

I don’t understand where the switch is supposed to be…on the car? or wired to the charging base?

4

What you want to do can be done with a relay, arranging that
the relay also provides voltage to the solenoid. When you hit
the button, the relay triggers and the relay then keeps itself
triggered until you break the solenoid circuit with a separate
normally closed switch.

Eugene

5

Could you just use a toggle button?

If not there is a component called an SCR you might be interested int. Its basically an electrically controlled switch that once turned on via a trigger lead does not turn off again until you disconnect the load.

6

Dr Brooks’
Relay suggestion is a classic design that goes from completely off to a simple latch that supplies power to the unit. Haven’t seen that one since I worked on Telephone switching equipment in the days before calculators! But hey it’s cool and simple and does the job and I’d go with that suggestion if you need to be completely un-powered while waiting.
The same basic design can be implemented with a flip flop latch arrangement or even a 555 timer but these need at least some power or a preset state for power on.
If you can have battery power then in the case of a PIC or Basic Stamp chip you could just have it looping until it see your momentary button and it can power everything else up.
Point is, there are many ways to do this but I think you need to give more details.

Best Wishes

Steve Alaniz

7

Jose,
Doc’s suggestion is the simple approach and requires no additional circuitry. You don’t need to add something to turn it off since it will reset when you remove the main power. What you need is a small relay with SPST contacts. You should be able to get this at Radio Shack in both 5 volt and 12 volt versions. You wire one of the relays contacts and one side of the relay coil together with the positive side of the power supply on the vehicle. Then wire this connection to one side of the start button. Attach the other side of the relay coil to the negative terminal of the power supply. Then connect the positive side of the power supply to the second contact on the relay and the second contact on the start switch. When you press the start button, the relay pulls in and supplies current to the vehicle and the relay coil which holds it closed until the power is removed. The relay needs to be on the vehicle but you can wire the start button through the charging stand and the same kind of connector you are using to supply charge current to the vehicle.

8

The relay is classic for this type of application.

If you were using a microcontroller like the PIC in the FRC RC you can do the following:

Connect a loop of wire through one of the “disconnecting” connectors. Call this the docking sensor. Connect it to any input of the PIC.

Connect a start switch through the “disconnecting” connector to a portB input.

Upon reset check the state of the docking sensor. If the input is 0 then you are docked and put the processor into a “low power mode”. The PIC processor supports this, the processor is effectively off.

When you close a start switch the processor gets woken by an interrupt that somthing changed on portB, if it was the start switch, wake the reset of the robot/car using a relay/breaker (like a spike relay), if not go back to sleep.

This is really closer to what happens on modern motherboards today.

9

Jose,
In reading back over my previous post, the first instruction might be a little confusing. The relay coil and one of the contacts on the relay should be tied to the power input on the vehicle not the power supply (fuel cell and/or battery).

relay.jpg


relay.jpg

10

Thank you to everyone who responded to this. Ok, first and foremost, I understand the relay-based posts, and seems like something I can do, but just in case my description wasn’t clear enough, allow me to rephrase.

This is a video of the car which won the Northeast Hydrogen Fuel Cell Car Regional Competition.

You’ll notice in the video I was charging right to the last few seconds until the start of the race.

When the car crossed the finish line, the guy who I asked to stop the car crushed the chassis and bent the front axle–not exactly something I want to happen.

I want to improve the design so that all I have to do is plug the car into the charging station, go to the finish line with the push button in hand, push the button to start the car, and catch the car myself when it crosses the finish line.

The car is charging throughout the entire before-the-race period. When I press the button, the car’s circuit changes in such a way that the onboard fuel cell is not being charged anymore, but is instead discharging itself into the motor, thus making the car move.

As the car moves away from the charging station, the plug(s) disconnect and the car is now accelerating untethered toward me at however fast it will go.

I could develop some sort of automated stopping system (I’m thinking reed switches) but I’ll save that for later.

There are two main components to this whole system:

  • The fuel-cell powered car itself
  • The charging station

The fuel cell car obviously has a fuel cell which electrolyzes the water separating it into hydrogen and oxygen. It takes 4 volts max (as per the manufacturer’s specs) any more may destroy it. So, I either have a DC-DC converter on the car, or in the charging station. The car also will have some sort of plug (similar to the speaker plugs found between headphones and iPods, but easier to separate). That way, as it’s starting, the plug connecting the car and charging station separate, and the car races down the track untethered.

The charging station needs the plug, or similar energy-transfer device, and the power source, in my case, probably a battery. The push button is also connected to the charging station. Using either remote control or a really long wire, I bring the button with me to the finish line, and start the car from there.

I’m looking at the relay information on Wikipedia, and from what they post, the relay I’m looking for is something with similar properties to the latching relay. I then wire the charging station so that the main power goes into the control and source (I think that’s what it’s called) terminals on the relay. The source’s other terminal then leads to the fuel cell, while the push button/momentary switch goes between the source and control. When I push the button, the relay changes position, disconnects the charging station, and redirects the electricity flowing from the fuel cell into the motor.

11

Jose,
The circuit I included in my last post is an electronic latching relay and the remote start button can be off board the car and connected through a second connector which is the same as the power connector you described. You can purchase a real latching relay that will not drop out with low voltage but they are more expensive and you must supply power to get them to unlatch. Relays speced at 5 bvolts will pull in at a lower voltage perhaps as low as 4 volts. They will remain pulled in until the specified “drop out voltage” which you will need to look up. These specs vary with design and manufacture. You could also replace the relay with a power MOSFET powered by the fuel cell. An SCR might also work but will have a forward voltage drop that will take away from the motor.

12

A double pole double throw relay wired as a latching relay would work. Also,
a bumper micro switch wired as normally on could interrupt the latch circuit and de-energize the coil stopping the car when it hits your foot.

13

Ok, I mulled it over a bit and came up with the following circuit. (See attachment)

The toggle switch on the right is meant simply to arm/disarm the car itself so I can’t have a false start without first arming the car.

The two wires on the right lead to the charging station. The charging station is simply a battery pack with a regulated 3v going into the system in order to charge the fuel cell.

I wasn’t sure where to put the normally closed momentary switch. I figured as close as possible to the motor was best. Is that necessary?

Other than that, I think I’m set. I used ExpressSCH for circuit (http://www.expresspcb.com/ExpressPCBHtm/Download.htm)

One last thing. Is there anything wrong with this circuit? Will it perform as I want it to perform?

New Circuit.pdf (8.56 KB)


New Circuit.pdf (8.56 KB)

14

The purpose of that switch is to interrupt the power to the relay coil and permit it to turn off. It should be placed between the Normally Open relay contact and the coil. It would also work if placed between “+” side of the fuel cell and the common relay contact, or if placed between the other side of the coil and the “-” side of the fuel cell.

By the way, I’m a little confused about what the “fuel cell” actually is. You’re describing it as something which needs to be charged from an external electrical supply, but my understanding of a fuel cell is that it uses chemical fuel to produce electricity, and gets “charged” by filling it with hydrogen or alcohol or some hydrocarbon.

15

Ok, about the Fuel Cell, this is how it works.

The fuel cell is something called a Reversible Fuel Cell.

Namely, The fuel cell not only combines the hydrogen and oxygen to create electricity, but it can also separate it. The problem with this is that the fuel cell is about 40% efficient. For every joule of energy I put into the fuel cell, I can only get .4 joules out.

If you have any more questions about the fuel cell, feel free to PM me

16

Jose,
The circuit should work except for the momentary switch in the motor circuit. That switch is redundant with the toggle switch just below it. You can wire the momentary, normally closed, switch in either lead of the relay and pushing it will release (open) the relay.

17

Thank you Mr. Skierkiewicz and Mr. Anderson for your inputs. I’ll go hunting around for parts which would work for my 3v system. Hopefully, I can get what I need out of this to make it work. I’ll get back to this board with the results. (Digikey, radioshack, ugh…)

EDIT: On a completely random side, I’m working on a duct tape prom outfit with my date. We figured that we needed to be really shiny or otherwise bright at the prom itself. That led me to electroluminescent wire, also called glowire methinks. Anyway, how best should I attach the electroluminescent wire to the duct tape prom gear? Clear tape? Staples? Magic?

18

You might look at Lynx technologies and their key chain transmitters and a receiver with a latching decoder chip. They’re 3 volt devices.

19

Jose,
I have seen Duct Tape Tuxedos, are reallly sure you want to do this for a once in a lifetime event? Some tapes are conductive so you have to be careful how and what you use for ligthing. There are a few companies that manufacture LED ropes and light bars that might work. Clear tape would be OK. I would think that a few well placed thread stitches would be OK as well but why not use mini tie wraps? If you are stepping over the line of fashion you might as well take a big jump over the line.