Servo project: Help please.....

[hanim]

Hi, I have to do a small, simple project as part of my research study but has little knowledge of electronics. Wonder if anyone could help me

I need to do a simple device that can automates an occluder (plastic paddle) to test human vision. I have to control the occluder so that it rotates from 0 deg to 120 degree. Ideally it should have a switch (like a push button) to control the position/rotation. The system should be able to rotate the occluder in fast manner and less noise. Considering the plastic paddle is not heavy (weight=plastic ruler!!), I thought economy standard servo would be a good option to start off with.

I tried to put together a standard servo with a servo pot controller and it seemed to work. However, the setup uses a rotary switch and I want to be able to control it using a push button. I know I need a pair of resistor, but have no idea which one to use. Here are the components I bought!

Servo:
**broken link removed**
Specification:
Dynam model B2232.
Weighing =34g
Torque 3.2kg-cm at 4.8V @ 4.1kg-cm at 6V
Speed 0.23 sec/60 degree at 4.8V and 0.16 sec at 6V
Size 55 x 20 x 45mm.

Pot servo controller:
**broken link removed**
Specification:
Supplied complete with a 10k pot, interface, leads and a battery connector that will fit our AA battery holders. Requires a 6V supply.

Apart from the 'resistor problem', can anyone suggest what should I buy to house all the electronics parts as I need to attach it to a metal bar, vertically. I am also not sure if it is save to drill the plastic occluder and attach it to one of the servo arms and whether this will affect the servo speed.

Thanking in advance for your help.

 

[MikeMl]

Assemble it. Set Pot to desired position 1. Temporarily disconnect pot from circuit and measure Pot Ω both end-to-end and wiper-to-ground end.

Reassemble, set Pot to desired position 2. Temporarily disconnect POT and repeat measurements as above.

Write back with three numbers: resistance end-to-end, resistance wiper-to ground end for both position 1 and postition 2, and we will work out a network consisting of a toggle switch and either two Pots or fixed resistors.

It may be as simple as getting a second identical Pot, and then using a form C SPDT toggle switch to switch between the wipers.

 

[hanim]

Thanks MikeMI for the reply..
I know this may sounds silly but do you mind explaining how can I measure the resistance? In other words, what do I need?
We have a technician here in the department but he is not familiar with electronics stuff. It is better if I know exactly what I need, so I can just go to the shop and buy one (just in case if we don't have it in the dept)

Really appreciate your help!!
Many...many...many...thanks!!

 

[blueroomelectronics]

You'll need an Ohmmeter or Multimeter.

 

[MikeMl]

You'll need an Ohmmeter or Multimeter.

Looks like one of these

 

[pcbheaven.com]

it has 3 pins. Thus, you will measure 2 resistanse. One is the mid pin with the left and another the mid with the right. You will need therefore to add 2 resistors (one from the middle to the left and one from the middle to the right).

 

[hanim]

Thanks guys!
I'll do it today.

 

[pcbheaven.com]

it might help you some servo theory

**broken link removed**

 

[hanim]

Hi again,
I've finally got the servo working (the way I wanted it to be!). Thanks to you guys for all the advise! I have mounted it on a metal bar (vertically), control it with a manual switch and it can 'safely' be use as an automated occluder to test human vision. However, I'm facing a new problem now as to how to detect the movement of the occluder from OFF position (no occlusion) to ON position (occlusion). Would using a photodiode sensors solve this problem? Can anyone help?

 

[Mr RB]

Try a lever style microswitch.

 

[marcbarker]

Hi again,
problem now as to how to detect the movement of the occluder from OFF position (no occlusion) to ON position (occlusion).

Maybe I'm missing something... Isn't the whole idea of a servo is that it already knows where it's pointing? It should be where ever it is pointed to, according to the command given to it. The servo already knows where it is, there's a position sensor inside it.

 

[hanim]

Hi Mr RB,
Similar to this one?

**broken link removed**

Look sensible to me but would you mind helping me with the circuit? I am clueless...

 

[hanim]

owh..you're right, marcbarker. It did rotate to the right angle/position but I need to detect 'when' it reaches to that ON position so we can interface with a computer programme and time-stamped the movement.