Hardware recomendations needed ?

[Steve Roks]

Hi and thanks for all the help so far, the forum's have been extremely usefull in finding information related to my project.

I recently purchased the isopod hot deal and my programming dude's have got servos up and moving while I try and figure out the wiring.

My project is to buld a wireless remote camera head; 2 axis controlled by encoders, and 3 axis controlled by potentiometers. The 2 axis encoders would controll pan and tilt with dc motors and h bridge and the 3 controlled by potentiometer's would control focus,iris,zoom and be dc servo motors powered off the isopods rc motor adapter board.

I plan on using two isopods one for input of 2 encoders, 3 potentiometer's and a relay for on/off and the other for controlling the motors and possibly encoder feedback for accurate positioning. The two pods will be connected via rs232 during development and I will swap out the cable for rs232 transmitter/reciever when development is finished.

my questions:

- what type of encoders would work with the isopod (specs)? How would you wire them to the pod (do they take there powere from the pod)? When you use the rc adapter board it covers over the pins for encoder input ...?

- what type of potentiometer would be best ? Does it take it's power from the board ? How do I wire it to the isopod ?

- how do I connect two isopods using the j4 connector for rs232 communication ? How do I make one a slave the other a master ?

- how do I connect the relay to the pod ?

Thanks in advance,

Steve

[Dave]

Encoders that work with the IsoPod and other "Pods" are quadrature encoders. Usually all that is needed is the A and B channels of these to get feedback on specific registers of the IsoPod. They are generally powered by 5 volts (available on the IsoPod), and deliver 5 volt TTL signals, which can still be read by the 3.3 volt logic of the IsoPod. The RC servo adapter still has the TimerA0 (PhaseA0) and TimerA1 (PhaseB0) that would be attached to the encoder pins.

Potentiometer would probably be best in the Kohm range, to limit the amount of current used. It sould be attached between ground and 3.3 volts to match the AD limits, with the wiper to AD pin used.

For RS-232, I believe that connecting Rx of one to TX of the other, and then using appropriate programming to initiate communications.

A relay could be connected to the IsoPod with the use of a transistor. The IsoPod could be connected to a logic level N-channel FET, which then would energize a relay coil. It might be required to have a buffer of some type like a 5 volt logic gate to switch the FET better.

[Steve Roks]

Encoders that work with the IsoPod and other "Pods" are quadrature encoders. Usually all that is needed is the A and B channels of these to get feedback on specific registers of the IsoPod. They are generally powered by 5 volts (available on the IsoPod), and deliver 5 volt TTL signals, which can still be read by the 3.3 volt logic of the IsoPod. The RC servo adapter still has the TimerA0 (PhaseA0) and TimerA1 (PhaseB0) that would be attached to the encoder pins.

I have found some encoders on US digital's website that I think will work
http://www.usdigital.com/products/s1s2/
They come with and without an indexer ? Not sure what difference this makes to the pod (I think there's a pin for it?)
- Can I take the 5v from the J6 connector on the pod, the pin next to the phase pins (ie: pin 2)?

Potentiometer would probably be best in the Kohm range, to limit the amount of current used. It sould be attached between ground and 3.3 volts to match the AD limits, with the wiper to AD pin used.

- which connector and pins should I take the 3.3 v from on the isopod ?
- wiper should be connected to the J3 connector on the #3 pin ?
- is vref (pin #1) a ground ? ( on the J3 connector )

For RS-232, I believe that connecting Rx of one to TX of the other, and then using appropriate programming to initiate communications.

- how do I make the appropriate cable ? (which pins on J4 do I hookup to a dbf9 cable to access the second rs232 port )

A relay could be connected to the IsoPod with the use of a transistor. The IsoPod could be connected to a logic level N-channel FET, which then would energize a relay coil. It might be required to have a buffer of some type like a 5 volt logic gate to switch the FET better.

- would an H bridge be an easy solution ?


Thanks in advance,

Steve

[Dave]

Yes, the US Digital encoder should work fine. And you can take the 5 volts from the pin mentioned, but the RC-servo adapter might be in the way.

ADC0 is pin3 on J3 and should be fine to measure the wiper, and pin3 on J5 has 3.3 volts that could be usable.

Making a cable for RS-232 should just be 3 wires with female pins for Rx Tx and Gnd to connect the IsoPods.

An h-bridge could be used to drive a relay, but only half the h-bridge would be needed. (pulling down the relay connected to power).

[Steve Roks]

Yes, the US Digital encoder should work fine. And you can take the 5 volts from the pin mentioned, but the RC-servo adapter might be in the way.

:)

ADC0 is pin3 on J3 and should be fine to measure the wiper, and pin3 on J5 has 3.3 volts that could be usable.

Making a cable for RS-232 should just be 3 wires with female pins for Rx Tx and Gnd to connect the IsoPods.

- pins 5,7,9 on J4 or 1,3,5 on J4 ? (would pin 1 on first pod be connected to pin 3 on second pod, and pin 3 #1 pod to 1 #2 pod ? )

An h-bridge could be used to drive a relay, but only half the h-bridge would be needed. (pulling down the relay connected to power)

could you use one h-bridge to control two relays ?.

- Do you have any answers on the indexer for the pod and encoders ? (will the pod accept the signal ? , is it neccesary for the pod to recieve the indexer signal ?)


Thanks again :)

[Dave]

For RS232 levels use pins 7 and 9 with 5 as Gnd. If TTL level serial, then pins 1 and 3 with 5 as Gnd. Essentially use the same set of pins on one that you use on the other, switching the INs and OUTs between the 2. Use the RS232 pins for longer distances, and the TTL levels for short runs.

Yes, one h-bridge can control 2 relays as long as the coils do not require more current than the h-bridge is capable of.

[RMDumse]

The index output on the encoder is an additional signal which can be used to reset the count to zero when it passes that mark. This is to eliminate the problem of "slipping" counts on the encoder and loosing absolute position.

There is also usually a home signal which is similar, which allows a mechanical position to be backed up until it returns "home" and represents (usually) a mechanical stop at one end of its travel.

Since encoders don't have an absolute position output, only "step and direction" which are integrated to get a position, these additional signals can be used to get an absolute position. Generally the home position is more useful than the index signal with the high quality counting possible with these registers, as long as the signal doesn't get too noisy.

The Pod's hardware encoders have two pins that can be used for index and home inputs with the encoders (also called TA2,3 and TB2,3), but these also have valuable timer functions they can be used for (even more encoder functions), so most don't use those functions with the hardware encoders.

[Steve Roks]

Thanks again for all the help :)

"Since encoders don't have an absolute position output, only "step and direction" which are integrated to get a position, these additional signals can be used to get an absolute position."

I need the encoder to work in both directions and wonder if the pod is able to interpret the direction of the encoder ? The encoder I was thinking of using was the s2 -1000 from us digital
http://www.usdigital.com/products/s1s2/
I need to hook 2 up and recieve cw / ccw signals from both. (one for pan axis and the other for tilt axis )


Steve

[Dave]

Using only the A and B channels of the encoder will get you direction and distance. The A channel is typically 90 degrees out of phase with the B channel. When turning one direction, A leads B, turning the other, B leads A. The hardware of the IsoPod is such that there is a register that increases in count or decreases in count according to the direction the encoder is being turned. This can be done directly for 2 encoders, using the pins PHASEA0 and PHASEB0 for one encoder, and PHASEA1 and PHASEB1 for the other.

If the controller is powered down, and then the pan/tilt mechanism is moved, then all position information is lost and the count will restart at zeros where ever the camera is currently pointing when the unit is repowered.

[Steve Roks]

thanks for the info and your time, I will be busy the next while ordering and hooking things up. I will let you know how it goes... I bet I have a few more questions..lol , and my programmers...lol

Steve

[Steve Roks]

when hooking up an analog input to the J3 bus do I need to hook up anything to the vref pin (pin #1 on J3) ?

[RMDumse]

No, the J3 offers Vref as an output, the analog 3.3V. I think there is a cut you can do on the board if you want to feed a different Vref, but usually, it's just there in case you need the maximum voltage. For instance, it makes adding a pot for mechanical feedback very easy. You'd hook up two ends of the pot to Vref and Agnd, and the wiper to the A/D input line.

[Steve Roks]

"the J3 offers Vref as an output"

- can I use vref as the 3.3 v input on 3 potentiometers ?
- what is the vssa pin (J3 pin 2 )?


I hooked up a 1k potentiometer to the pod, I took 3.3 v from J5 pin 3, GND from J2 pin 4 and the wiper goes to J3 pin 3. Now it's up to the programming dudes to figure it out.

- should I change this wiring configuration ?
- is there a better place to take the gnd from ?

thanks in advance,

Steve

[RMDumse]

Well, you can pick up 3.3 whereever you like. You will get quiter and better results using the Vref and Agnd from the A/D connector.

The analog side of the board is separated from the digital side of the board with inductors to try to get rid of the digital noise. By picking the voltages and gnds elsewhere, you will be bringing in several bits of noise with your signal.

1K is on the small end. If you parallel several pots at 1K, you can overtax the current available from the Vref. Well, it's only 3mA each, so maybe this isn't much of a concern. On the other hand, the lower the value of the pot, the lower the impedence into the A/D, and the quieter the signal should be.

[Dave]

Vref and Vssa (analog ground) on J3 should be fine to use. The Gnd on J2 does not have the inductor that helps in noise limiting. Note however that 3 1K pots in parallel would produce a 10 mA current draw, not much, but it adds up. It should work fine as is, but should work with 2K or 5K pots too.