Urgent help needed in schematic Diagram

[codename25]

Hi,
   I am confused about the schematic diagram of pololu 3Pi robot.Values of the components marked by RED CIRCLE are not given in the Schematic attached with this post, ie:(U4-U8,Q4,capacitors used in Y1),If anyone can help me by telling me What it is & value for that component etc...Will be great.

The direct link to the schematic diagram is: http://img693.imageshack.us/img693/7016/0j1164700.png



Thank you!

[Soeren]

Hi,

Y1 is a 20 MHz ceramic resonator.
U4..U8 are optocouplers (all the same I suppose).
Q4 is a small N-ch. MOSFET - any that fits correctly (w. respect to S, D and G) will do, it's just for controlling the LED's in the couplers on/off.

The values you must know if you bought the kit?

[codename25]

Thanks for the reply,Would you please specify the value of Q4.bcoz im a beginner to this field and also the value of optocouples.
Thank you!

[Soeren]

I'll repeat... "The values you must know if you bought the kit?"

[codename25]

No,I didn't bought the kit yet.

[billhowl]

The U4-U8 is not optocouplers but a reflectance sensor as shown in the Pololu 3pi Robot User's Guide.

http://www.pololu.com/docs/0J21/5.d
QTR-1RC Reflectance Sensor
QTR-8RC Reflectance Sensor Array

the Reflectance Sensor Array came with the MOSFET installed.
If you need Logic Level Gate N-Channel MOSFET you can get this 2N7000 60V 200mA
http://www.fairchildsemi.com/ds/2N/2N7000.pdf

[codename25]

So, can i use photo transistors like PNZ154, PNA1605F, BPW77NA or BPW85 in this circuit???and what should be the color of the LED used in the Reflectance sensor.

[billhowl]

 The LED is infrared LED as listed in the 3pi User's guide and you can try the listed photo transistors and wired as show in the circuit.

[codename25]

Is there any alternate motor driver for TB6612FNG?Why are they giving Vboost (9.25v) to the IR led array instead of Vcc(5v)?

[billhowl]

For motor driver you can use L298 but is not as efficient as the TB6612FNG which used MOSFET switch with low ON-resistance of 0.5 ohms, as for

Why are they giving Vboost (9.25v) to the IR led array instead of Vcc(5v)?

This is listed in the manual

at 9.25 V, all five of the IR LEDs can be powered in series so that they consume the lowest possible amount
of power. (Note that you can switch the LEDs on and off to save even more power.)

[Soeren]

Hi,

The U4-U8 is not optocouplers but a reflectance sensor [...]

A reflectance switch is an opto coupler (just like a MOSFET is a transistor).

[codename25]

TB6612FNG is not available in my local market.So, i decided to switch on to L298 as motor driver as an alternate for TB6612FNG.But, I don't know to make the connections to the circuit.How should i make connections by replacing TB6612FNG with L298 in the circuit i have given?


http://img693.imageshack.us/img693/7016/0j1164700.png

[waltr]

TB6612FNG is not available in my local market.So, i decided to switch on to L298 as motor driver as an alternate for TB6612FNG.But, I don't know to make the connections to the circuit.How should i make connections by replacing TB6612FNG with L298 in the circuit i have given?


http://img693.imageshack.us/img693/7016/0j1164700.png

The two motor drivers are close but not exact replacements. Look at the input to output logic diagram on the data sheets for both driver chips. Then try to match up the input pin functions. Post a question if need clarification.

[codename25]

If i want to change the tb6612fng,i should change all the pins connected to Atmega168 because in 3pi robot they have connected the pins in a separate manner Eg:PINS 33-40 has ADC7-ADC0 (as in ATmega16 datasheet) while in 3pi the ADC0-ADC3 are in the pins 23-26.

[codename25]

I have tried connections for L298 instead of TB6612FNG.But i have some doubts on pins 6,11(Enable A,Enable B.recpectively) in L298,Where should i connect it?to Vcc or to microcontoller?
The coonections i have made to L298 are given below:

Pin 1:Ground connection

pin 2: output 1

pin 3: output 2

pin 4: Vs-12v to 45v

pin 5:Input 1

pin 6:got confusion on where to connect

pin 7:input 2

pin 8:ground connections

pin 9:Vss-5v

pin 10:input 3

pin 11:got confusion on where to connect

pin 12:input 4

pin 13:output 3

pin 14:output 4

pin 15:ground connection




             

[waltr]

See figure 6 in the L298 data sheet and look at the logic diagram.

You could tie the enable line high (Vcc) if you don't need to disable the outputs to the motors to let the motors free wheel.

You can get the three necessary motor controls (Stop, Forward, Reverse) from the two inputs, C & D. This would get the same functions as the way the TB6612 is wired on the schematic you are using.

[codename25]

So i should connect the enable A,Enable B (6,11) to the Vcc(5v) in order to get the same functions that TB6612 gives.Well, Please check Whether the other connections i gave are correct?I have connected the sense a,sense b(1,15) to ground.any problem with that?

[waltr]

I don't believe that connecting the two sense pins to ground is a problem.
 The L298 data sheet does show an example circuit for current sense but any action is totally external to the L298. The L298 sense pins are the return current path from the H-bridges to the power supply.

[Soeren]

Hi,

I don't believe that connecting the two sense pins to ground is a problem.

No problem at all. They're just an option, if current regulation is needed/wanted (which is a really good idea if stall current is more than what it can handle).

[codename25]

In 3pi robot i noticed that the micro controller used (ATmega168) which has 40 pins are configured to connect as below:

pin no.                              pin configuration

1                                      PD3 (OC2B/INT1)

2                                      PD4 (XCK/T0)

3                                          GND

4                                          VCC

5                                          GND

6                                          VCC

7                                      PB6 (XTAL1/TOSC1)

etc...


while in the Atmel's Atmega168 datasheet the pins are configured as given below:

Pin no.                                               Pin configuration

1                                                     PB0(XCK/T0)

2                                                     PB1(T1)

3                                                     PB2(INT2/AIN0)

4                                                     (OC0/AIN1)PB3

5                                                     (SS)PB4

6                                                     PB5(MOSI)

7                                                     PB6(MISO)

etc....

i would like to know whether both these connection configuration are same?and whether is there any problem for using the pin configuration as given in the 3pi robot (i mean,whether it will damage the ATmega16)?