controller circuit help

[Crazy Lee]

Wow. Forgot this board existed.

Anyway. @Lopaw, anyone else who knows electronics. I'm trying to set up something electronic for the holiday.

The details are thus:
The device I have has a 5v or so power, a ground, and most importantly, a signal or "mode" pin. The pin allows you to switch modes in the chip-controlled device. Now, here's how the device works. You apply power to activate it, of course. It does a quick start up cycle and then stays on in the first "mode". Every time you ground the mode/signal wire, it switches modes. I considered using a 555 circuit to ground it on a regular cycle (and maybe a pot or rheostat to adjust the cycle frequency). Here's the thing though. The cycle for the device every time the mode wire is grounded is "mode 1-off-mode 2-off-mode 3-off...." in other words it turns off in between each mode. If you ground the pin it either goes off or to the next mode. Also, it doesn't matter how long you ground the pin, it only switches each time it's grounded. So you could ground it for 10 seconds and then stop and it would only switch once.

Honestly it seems easiest to control with a microcontroller board. But, I wondered if some kind of IC setup could run it as well.

Anyway, something I'm working on.

[Jerry]

If I understand you would need to ground the pin twice per cycle so that it jumps the OFF each time, right?

You could achieve this by cascading two astable 555s, (a 556 dual timer chip would be even better). One at a slow frequency (say once per 5 seconds or 0.2 Hz) triggering the second 555 just for long enough to generate two short pulses.

As for the exact schematic I guess I can sketch something out real quick.

[Lopaw]

Using a microcontroller and programming it to output a decent clock signal will be easier than setting up a 555 or 556 with the external resistors and capacitor each timer needs to work in astable mode, you'll also need a decoupling capacitor between the 555's VCC and ground pins to have it work properly, most diagrams of 555 timer setups omit this as it is assumed to be there. If you are going with the IC setup.

An microcontroller will give you easier control over the duty cycle and frequency I imagine. Sending the output signal to the base of a decent NPN transistor with the mode pin connected to the collector and the emitter connected via a pull up resistor to ground should allow you to control your mode changing thing.

[Crazy Lee]

4 hours ago, Lopaw said:

Using a microcontroller and programming it to output a decent clock signal will be easier than setting up a 555 or 556 with the external resistors and capacitor each timer needs to work in astable mode, you'll also need a decoupling capacitor between the 555's VCC and ground pins to have it work properly, most diagrams of 555 timer setups omit this as it is assumed to be there. If you are going with the IC setup.

I had considered doing a pair of 555s (or a 556) to do it but realized it's rather complicated. Plus, I am a noob when it comes to electronics. But I figured it would be a challenge and I might learn stuff along the way.

 

4 hours ago, Lopaw said:

An microcontroller will give you easier control over the duty cycle and frequency I imagine. Sending the output signal to the base of a decent NPN transistor with the mode pin connected to the collector and the emitter connected via a pull up resistor to ground should allow you to control your mode changing thing.

I had considered just plugging the device's mode pin directly to the microcontroller (with proper resister.) The device draws current in the mA range, anyway. But a transistor would work, it would just require a separate board.

What's the pull up resistor, though?

[Lopaw]

On 11/12/2016 at 0:51 AM, Crazy Lee said:

I had considered doing a pair of 555s (or a 556) to do it but realized it's rather complicated. Plus, I am a noob when it comes to electronics. But I figured it would be a challenge and I might learn stuff along the way.

 

I had considered just plugging the device's mode pin directly to the microcontroller (with proper resister.) The device draws current in the mA range, anyway. But a transistor would work, it would just require a separate board.

What's the pull up resistor, though?

I mean to put pull down resistor, couldn't recall which it was.

A pull up resistor provides a load between the pin of what it is connected to and ground so that the pin doesn't "float" with whatever voltage may end up on it when it isn't currently receiving a signal. Protects the pin from ESD as well.

A pull down resistor is the same but connected between a pin and ground, normally to bias voltage down the wire it is connected to.

Pull ups are generally more common though.

And I may not be entirely correct, I have only been doing this electrical engineering stuff for a year and a bit.

[Crazy Lee]

15 hours ago, Lopaw said:

A pull up resistor provides a load between the pin of what it is connected to and ground so that the pin doesn't "float" with whatever voltage may end up on it when it isn't currently receiving a signal. Protects the pin from ESD as well.

Sounds like you'd want to put the resistor between the transistor and the output pin, then?

[Lopaw]

On 13/12/2016 at 10:36 PM, Crazy Lee said:

Sounds like you'd want to put the resistor between the transistor and the output pin, then?

A small value one may or may not be needed. Is this chip controlled device part of something larger or is it the chip itself? Part numbers would be useful so I can find a datasheet. 

Where is this signal being taken to from the output? Because the transistor is going to draw a small amount of voltage away from your signal when it saturates and some things are fussy about signals being within a certain range.

[Crazy Lee]

Datasheet huh? Yea, there's a "datasheet" of sorts, but it took forever for me to find it. I'll try to find the file, or figure out where to post my copy of it.
Edit: Nevermind, googling the numbers I had on file made it pretty easy. http://www.alldatasheet.com/datasheet-pdf/pdf/184695/MICRO-ELECTRONICS/MSGBB557TA.html
It has a range of 2.5-3.5v, peak amps 35 mA, so not a heavy draw at all.

I'll probably run it off an Uno, because I have a spare one lying around and it's not going to require a lot of power.

I'm a bit frustrated because the local maker space was only open today and next Thursday and I'm busy both times. They have a pretty good selection of random circuit parts that would be useful.

Edit2:
The easiest way to run the device is to apply power and then add a switch to the mode pin. That's the manual way. I had considered doing an RC circuit but wasn't able to quite get it to work. I have seen a video where a guy looks like he uses an astable multivibrator (a device that uses two transistors and two capacitors to oscillate back and forth) to run two of them, but I'm not sure how he wired it. The pure hardware method would probably be two 555s or a 556.

[Crazy Lee]

Okay. Some tests on the led device show that it uses a max average of about 26 mA (not counting possible spikes my multimeter missed) and a min of 18mA, so I could run it directly from an arduino uno.

If I were to run it off an arduino, there's several options I could do. First, I could hook the v+ pin to a digital output pin (through a resistor), and put it to high if I want to turn it on. The output pins put out 5v. The ground would go to arduino ground, and the mode pin would go to a digital pin set to output and set low. When an output on an arduino is set low it creates a ground, or sinks the pin. So this would be adequate for what I'm doing.

A more complex version would be to have the v+ of the led hooked up to the 5v terminal on the uno, and have a transistor hooked to a digital output pin to control that transistor. The mode pin would also be hooked to a transistor and a digital pin. I am trying to figure out if there's a way to read if the LEDs are on or off. I have noticed when they are off, there is little power being used by the LEDs, so there's full 5v across the LED. With it on, the led draws 3v. So, I wonder if there's a way to sense this. Maybe using the analog pins on the arduino, or using a device that's triggered at a certain volts.

I still want to give the 555s a try just for the hell of it.