Gimzo 2 custom On/Off button?

Check out this post where I added an external power and reset button: http://www.element14.com/community/community/designcenter/single-board-computers/gizmo2/blog/2015/01/28/gizmo2-adding-external-pwr-and-rst-buttons

Oh wow, so much great tutorials I'm having hard time finding

So you didn't use a resistor?

Is there any requirement for what button can be used. All I know is buttons have a maximum current rating, this shows how little my electronics knowledge is. But it's going to be fun programming the Gizmo after I get this figured out.

PS. Is that a 3d printed enclosure? That's another hobby of mine.

I mean that as the pins for power and reset are specifically done for this scope, I suppose that as they don't mention extra-components the two buttons are sufficient.

Anyway: I have done experiments and an extra-component is needed as the bare button it works but is not debounced. So I need a small 555 to debounce the buttons. Those shown in the images was just a stupid test to see it working and evaluate the idea for a prototype. Also and external power is needed to manage extra SSD and extra fan and other stuff.

Enrico

I see , however, is debouncing a problem with the on/off button (not the reset)? I just need the on/off button myself.

And did I get this right?: resistor will help with debouncing? Sorry, my electronics is lacking.

It is a problem of both.

In the rest it is not so influencing as a repeating reset pressing does not generate more than multiple rest and the effect is anyway the expected (but it is not the best solution without debouncing).

While powering-off debouncing instead is meaningless: you should keep the power pressed for few seconds. Instead I have noted it has influence when you power-on.

Enrico

While powering-off debouncing instead is meaningless: you should keep the power pressed for few seconds. Instead I have noted it has influence when you power-on.

I'm sorry, can you p[lease reword this part?

And will the resistor be a solution for debouncing?

Debouncing is the phenomenon that happens when you press a button but as a matter of fact the responsiveness of the system if so fast that with some other factors the effect is like you press the button twice or more.

The resistor is for current limitation (or other usages, depending on the kind of connection respect the button) when the button signal - high - is put to ground to generate the I/O event. This has nothing to do with the resistor and - unfortunately - it is a bit more complex. few more but it is. Take a look to this link: http://www.labbookpages.co.uk/electronics/debounce.html Here is clearly explained what happens when you press a button and how you can manage the physical event avoiding the debounce with an OpAMP, a diode and a capacitor. The principle is that the capacitor generate a minimum delay in the button press (due it is charging) then when the OpAMP AND the button signal and the capacitor discharge the output event is effective. Also keeping some microseconds more the button pushed (that is you finger pressing reaction time) nothing happens because before a second event occurs it is needed not only that the button is pressed but also that the capacitor is charged.

I suggest to try with a breadboard the case of the power off, that needs the button pressed for some seconds. The interesting aspect of the example circuit in the link above is that it shows a schematic with acceptable values for the discrete components.

Enrico

Sorry the OpAMP is a schmidt trigger to be precise (it is impossible to edit the comments ?)

I understand. But will that be an issue for the on button? To turn off you have to press and hold the same button for few seconds. Not like debouncing would changing anything here, right?

Frankly I suppose this can represent a problem but to be sure in this particular case (it is the first time I do this on a Gizmo2) I should test it. My suggestion is to add the resistor and ignore the debouncing circuit. This can be done in minutes with a breadboard. It is probable that this works as I suppose.

The debouncing effect is almost common with push buttons and can be solved - as shown in the page I got you before - via software or hardware. In this case it is not possible to solve it by software so a small circuit should be done. For more detail on how the debouncing should be implemented and why this occur, take a look to the following pdf: http://www.eng.utah.edu/~cs5780/debouncing.pdf

So im confused, you think debouncing will be an issue here, or the opposite?

Hi Mark,

Enrico is suggesting try it with a resistor, see if it works for you.

If you observe some behavior that is undesirable (e.g. having to hold the button pressed for a long time) then it can be considered further and you then may need a more complex circuit.

His linked article is extensive, and provides much detail on how different debouncing circuitry works.

Whether you actually need delays, debouncing, etc., can be answered in detail either by Gizmosphere (since they designed the board), or a detailed examination of the circuit and the power management IC user guide (which would require some time to investigate). An alternative approach (as suggested by Enrico) is to just try it, observe the results and see if it fits your required button-press behavior.

Hi Mark,

Enrico is suggesting try it with a resistor, see if it works for you.

If you observe some behavior that is undesirable (e.g. having to hold the button pressed for a long time) then it can be considered further and you then may need a more complex circuit.

His linked article is extensive, and provides much detail on how different debouncing circuitry works.

Whether you actually need delays, debouncing, etc., can be answered in detail either by Gizmosphere (since they designed the board), or a detailed examination of the circuit and the power management IC user guide (which would require some time to investigate). An alternative approach (as suggested by Enrico) is to just try it, observe the results and see if it fits your required button-press behavior.

Thanks shabaz

Sorry that I didn't get what you meant the first time. Thanks.

EDIT: Oh wow, I confused the original post by Frederick Vandenbosch with Enrico Miglino because both of you had similar minions avatar, thats why I felt I was getting contradicting info from you.

Sorry for being a bit too cautious.

The power on/off pins are these, right (highlighted in green)?:

And does the size of the switch matter? (different current from different resistance or something?)

And hopefully last question: if I want Gizmo to autostart, just use a simple jumper with resistor for these two pins?

The first answer is yes.

The second answer is no. The pin simply send a signal based on the pull down as it is pressed and connects the high signal to ground then this input signal tells to the boot firmware to start the boot process, load the bios etc.

To have the system autostart you should know how and modify this internal part of the firmware. In theory it is possible, just with the programmer and the sources of this part of the Gizmo2 project. As the entire device is open source you should not have difficult to find the information and software that is needed. But what is the reason you need the system autostart? And autostart what does ti means for you? Something should happen to make the system to start, correct? What event ?

Enrico

Was the first answer also the answer to "does the size of the switch matter"?

Okay, here's the reason I was thinking of having autostart for the Gizmo:

1) The device is something like a light fixture consisting of 3 individual devices in one case:

1. a tiny video projector

2. Gizmo 2, which generates graphics and sends to the video projector

3. an Arduino (Nano), for having buttons to choose between media files stored in a USB stick and read by a program running on the Gizmo 2 and communicating with the Arduino via serial, as well as controlling a tiny shutter motor to block video projector beam in some instances.

So I need to turn on 3 individual devices, but want to have 1 button for that. It might be simple to create a circuit board for most of you to do this, but I don't have the skills.

Arduino boots and starts executing when Gizmo 2 does, if connected via USB. So no problem there.

Video projector is more complicated, it has a button you need to press and hold for 4 seconds for it to turn on. Sadly it can't autostart like the Arduino when power is applied.

Now, if Gizmo autostarted as well when I connected the (not stock) power supply, I could still have what I want ( 1 button for turning on (visibly on) the light fixture ) and pressing the turn on button would start the video projector, and everything else (Arduino and Gizmo) would be ready already.

But if autostarting Gizmo is not easy, I need some simple solution for powering both the Gizmo and video projector with one button.

One solution I have in my mind is having the power on button just start the Gizmo, and then emulate the 4 second button press by a DC-DC relay and the Arduino (soldering cables around the video projector's start button).

In my opinion you have the solution in your hands but you don't see it

Power on - Arduino starts

Then the first thing that Arduino should do one is power the projector, then power the Gizmo2 then Gizmo2 starts communication etc. etc.

How to? In both cases you need to connect the button that should be pulled to GND to one of the Arduino I/O and with a simple circuit based - for example - on a PN2222 transistor it is Arduino that do the job of powering on and off the systems.

To manage the long press on the projector, short press on the Gizmo2, long press on Gizmo2 for power-off all can be done (and must be) by the Arduino, that is just the board that - as it is a Micro Controller - has this role in your architecture.

The following link explain you very clear (with circuit) how to use and I/O digital pin on Arduino to simulate a push button switch using a PN2222 transistor: https://teachmetomake.wordpress.com/how-to-use-a-transistor-as-a-switch/

Enrico

If I dont find a right transistor on time, are there DC-DC relays which could be used for this?

Isn't that simple to me as it is to you I'm afraid.

Although I did find the transistor needed.

Helo Mark,

if you find the PN222 the solution is in your hands (at least the first part). The use of a relay is essential the same (the transistor is a realy). The difference is that with the realy you can switch digitally the relay and it can power on/off a different current. As in this case you need only to emulate a simple switch with a very low power the amplification and switching capabilities provided by a PNP transistor are more than sufficient. I suggested a PN222 because it is the one I use more frequently in this case but you can use it or any equivalent transistor, no matter for this.

At this point, if I were you I will try breadboarding a simple circuit with the transistor (as shown in the linked documents of the post above) and see if without any debouncing it works fine. At this point the transistor switch operation should be done by the Arduino board (the first powering on and the first device running). So, as the entire system get powered, Arduino start its loop and the first thing that should do once is just to change the state of the I/O pin you have connected to the transistor. It switches the Gizmo2 and then if needed you can do the same to switch automatically the projector.

As the projector needs the switch pressed for 4 seconds to start, the faster way to test the entire system is to use a delay(4000) in the startup Arduino script for the I/O pin of the Arduino connected to the switch of the projector. Then when all is working fine and you see that almost the hardware circuit is reliable you can optimise the Arduino code to make it more elegant and efficient.

Let me know what are the steps that you have not clear so I can try to find better words to explain what I mean.

Enrico

I understand this is basic electronics and I'm really sorry for asking here, it's just I have a deadline and didn't expect I'd need this knowledge until the end of the project. You're being very helpful. Thanks a lot man!

So two pins of the transistor are are connected before and after the On button of the projector, and the third pin is connected to the Arduino PWM pin which controls the switching of the transistor? Did I get it?