Hi Guys, I am new here and could do with some advice. Basically I know nothing about electronics so please bear with me.
I have a message display board that I need to modify. It works off four 1.5v batteries and has a remote infra-red sensor built in that allows me to change the message via remote control.
It has a power management system built in that activates the message board when it detects vibration or motion and that allows me to activate or change the message. After 30 seconds of no activity, it shuts down again to save battery power. The problem is that the motion/vibration sensor isn't sensitive enough and so i have to shake it for the device to wake up. What i want to do is remove the motion sensor all together...or by pass it so that the message board is live all the time and looking for a signal from the infra-red.
I am not worried about depleting battery power as I intend to link it to mains power. That bit, I know how to do but i cannot work out where the motion sensor is on the board so I can over ride or dismantle it. I think I may have found it but if i have then i am not sure how to by-pass it.
The image below shows the back of the board.
Now I used a soldering iron for the first time ever and disconnected the Peizo speaker on the right hand side thinking that it may have a vibration/motion sensor built in. But the message board continued to work but without sound. I reconnected it and looked at the little silver box with the black ball situated that has three legs attached just below the infra red receiver. I covered it in insulation tape just to make sure that it wasn't part of the infra-red receiver and the device continued to work. So either it is the motion sensor or i havent got a clue what it is. I desoldered it from the board and the device stopped working completely and so i reconnected it. If that little silver box is the motion sensor then can i remove it and replace it with some sort of connector to maintain the circuit and ensure that the device still works without a motion sensing requirement and if so then what sort of connector would i need.
If it isn't the sensor then where would it be....part of the infra-red bulb perhaps?? There is nothing on the other side of the board except for capacitors, resistors and another silver tube like device that might be the programming unit for the messages.

Many thanks for your attention.

 

That silver thing is the IR receiver:


Pinouts may vary, but it looks like Pin3 goes to what may be R1C1 (low pass filter) to a 3pin device on the back. When the sensor is off, they usually give a high voltage (See: Fig 1, page3, http://www.vishay.com/docs/82459/tsop48.pdf ). Now, I am not saying the Vishay device is the same as yours, but it may be similar. If you measure the voltage at Pin3, it should be between 3.3 and 5 V, most likely. I would recommend as your first step to measure the voltage relative to ground at that pin with and without motion.

FUTURE PLAN: Since a low level from Pin 3 = motion (again, probably), then removing the IR receiver and grounding the pad for that pin should give you what you want , i.e., constant on. For testing, I would use a 100 to 1000 ohm resistor so you don't create a high current short circuit.

Edit: The system could have other timers, so holding the IR output low may not stop it from turning off. If that is the case, then making it constantly on is more difficult.

John

 

Thanks John. I know very little about electronics. When I disconnected the IR receiver and the device stopped working, I did try reconnecting the pins in sequence (1 & 2, 1 & 3, 2& 3) but each time the device didn't work unless i reconnected all three pins.
What does 'grounding the pad' mean and where do i connect the resistor for testing?

 

Oops, I read that pinout backward. Pin 3 may be the + supply. In any event, measure the voltage between pairs of pins. It is likely pins 2 - 3 will read either a positive or negative voltage. If the black lead on your meter is on pin3 and pin2 reads +V, then pin 3 is probably ground. Conversely, if it is the other way around, thenpin 2 is probably ground. With the black still on the putative ground, test pin1 as the possible signal. The resistor would go between which ever pin you identify as ground and the signal pin.

The output can source 5 mA and the Vishay design is:


Shorting the output to ground shouldn't hurt anything. I would still use a 100 ohm resistor for the first test, because we aren't sure of the pin out, and shorting Vss (+5V or whatever) to ground might do damage.

John

 

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I think i have found the vibration sensor on the circuit board. I believe its a mini vibration switch sensor (see pic)

How can I bypass this or if I remove it then would i need to replace it with something to maintain the connection.

 

I think i have found the vibration sensor on the circuit board. I believe its a mini vibration switch sensor (see pic)

Come on, Kevin, please let those of us here on AAC in on why you think that is so.

First, you talk about motion sensor and now a vibration sensor. Which is it? Are you sure? Looking at that cylinder completely out of context it could be anything, including a quartz oscillator. Did you try the experiment I suggested? Why do you think it is a vibration sensor? As I implied above, anything you do to fake constant motion, or in the newest scenario, constant vibration, is likely to be negated by the logic/MCU's.

John

 

Ok just bare with me for a moment. As I said in my original post I know nothing at all about electronics and so a lot of the technical talk goes right over my head.
In my first post, I initially refer to the sensor as a motion/vibration sensor because I don't know how the device works. Either the power management is triggered by motion or by vibration. What i do know is that if I lay the devizes down on a table and tap the table then it kicks in to life. Two weeks ago,I emailed the manufacturer asking for technical details of how the device works and how it is triggered - motion or vibration and i have yet to receive a reply.
So to summarise, the device kicks in to life if you tap it and will stay live for 30 seconds when uninterrupted. It continues to remain live if I continue to tap it.
I haven't tried your recommendation yet because I have spent two days researching PCBs, circuits and components trying to familiarise myself with the technicalities of electronics. I now understand the codes on PCB's (C1, C2, R1, R2 etc). I now know what a capacitor does and how it works and I am trying to get my head around how a resister and diode works.
I have yet to get a meter to measure the voltage to the IR sensor as you suggested and I will need to figure how how the settings and switches work once i purchase one.
What I did do it to start looking at the board and googling the components to understand what each one meant and did and whilst I was doing this I found a component that looked very similar to the attachment that i posted earlier. Whether it is the same, I couldn't say but it was located in S1 on the PCB and I know know that S1 on a PCB normally contains a switch and wondered if it was the same as the link to component below.

http://www.amazon.com/SW-200D-Vibration-Sensor-Shake-Switch/dp/B007Q81STQ

As I said, I have contacted the manufacturers for technical details of their product but am still waiting for them to respond so I am a little in the dark at the moment.

 

Sorry, but I'm not quite awake enough to be able to completely read through your long posts.

In one short sentence can you say what you are trying to accomplish?

 

From what you describe and from the vibration sensor you link to, it sounds like the motion sensor (IR1) and vibration sensor are set up so that if either detects something, then the message screen is triggered. If the vibration sensor is normally open (as the ones linked to), then you could try shorting. If it is normally closed, then removing it will make the circuit believe something has been detected. That process is basically analogous to what I suggested for the IR sensor.

What worries me is the 30-second on-time. That "time-out" is probably determined by one of the chips (U1-U6), and it might not be that simple to bypass it. Something mechanical or electronic could re-trigger the device, say every 31 seconds or 29 seconds. The device may not be retriggerable. That is, you may have to wait for a timeout before retriggering.

Nevertheless, it would be nice to know how to electronically trigger the unit with either the vibration or motion sensor.

John

 

Thanks John, I did some research on the vibration sensor that i posted the link to and it seems that how it works is that there is a spring inside thats triggered by vibration and opens the circuit so for as long as the spring is vibrating it keeps the circuit open and when it stops moving the circuit is closed. So the spring vibrates for approximately 30 seconds before coming to a rest unless it is disturbed.
So what i might try first is as you suggest to short it and see what happens

 

Thanks John, I did some research on the vibration sensor that i posted the link to and it seems that how it works is that there is a spring inside thats triggered by vibration and opens the circuit so for as long as the spring is vibrating it keeps the circuit open and when it stops moving the circuit is closed. So the spring vibrates for approximately 30 seconds before coming to a rest unless it is disturbed.
So what i might try first is as you suggest to short it and see what happens

That switch , as you describe it, is normally closed. Shorting a normally closed switch does nothing. You would need to remove it or cut a lead to simulate activation.
John

 

Right i see. So i should desolder and remove it or just cut one of the pins?

 

Desolder is preferred, as you will probably want to replace it. Desolder one pin first and test with an ohmmeter to be sure it is normally closed ("on"). Then just leave that one pin disconnected to test the circuit.

John

 

Ok will do. many thanks for your help