Stepper motor control with PIC16F84A

[Exo]

The problem with all of this is that the 4 pics must communicate with the fifth pic to tell it what to display, and I don't know how to do this.

You could use simple serial communications. Nigel's tutorials have code to do rs232 in software on a pic.

 

[netbug]

Hi,

I have a new problem. I am using 5 switches connected to a PIC. One of them is the START button, and the others are options (A,B,C and D) to a question that appears on LCD. Sometimes everything works fine, but some other times the system assumes that I pressed C option, when I simply pressed START button. Please note that START button and option buttons are in different ports, and that the C switch isn't connected in the board yet.

Should this be a code error ? Or can this be a debounce problem ? You can find below the code of the first PIC.

Regards,
Pedro Cardoso

TRISA = %11111 '5 pins as inputs
TRISB = %00000101 'bits 0 and 2 as inputs

ton var Byte ‘ Stepper time on
toff var Byte ‘ Stepper time off
j var Word
tpd var Word ‘ Number of turns per day given by the stepper

sentido var Bit ‘ Direction of rotation
n_passos var Byte ‘ Number of steps
max_passos var Byte ‘ Maximum number of steps
start_stop var Byte ‘start/stop flag
valor_enviar var byte ‘ Value to send to 2nd pic
start_stop = 0

max_passos = 200 ‘ Stepper with 200 steps
PORTB = %00000000
PORTA = %00000

' Wait for start button to be pressed
loop_inicio:
If PORTB.2 = 0 Then
Goto loop_inicio
Endif

TRISB = %00000001
portb=%00000000

' Start transmitted to second pic
serout2 portb.1,16780,["S"]

'Choose na option (A,B,C or D)
loop1:

'Wait till a button is pressed
If PORTA.0 = 1 Then
ton = 1 ' Provisorio
toff = 0 ' Provisorio
tpd = 600
valor_enviar=1
serout2 portb.1,16780,["B",valor_enviar]

Else
If PORTA.1 = 1 Then
ton = 1 ' Provisorio
toff = 1 ' Provisorio
tpd = 800
valor_enviar=2
serout2 portb.1,16780,["B",valor_enviar]


Else
If PORTA.2 = 1 Then
ton = 3
toff = 3
tpd = 1000
valor_enviar=3
serout2 portb.1,16780,["B",valor_enviar]

Else
If PORTA.3 = 1 Then
' ton = 42
' toff = 18
tpd = 1200
valor_enviar=4
serout2 portb.1,16780,["B",valor_enviar]

Else
Goto loop1
Endif
Endif
Endif
Endif

portb.1=0
portb.2=0
portb.3=0

'Os botões, a partir de agora, ficam inactivos excepto o do sentido
TRISA = %10000

ton_seg = ton ' Provisorio
toff_seg = toff ' Provisorio
n_passos = 0

' Rotation direction (CW or CCW)
If PORTA.4 = 1 Then
sentido = 1
Else
sentido = 0
Endif

loop2:

If sentido = 1 Then
Gosub motor_run1
Else
Gosub motor_run2
Endif

ton_seg = ton_seg - 1

If ton_seg = 0 Then
If toff_seg <> 0 Then
PORTB = %00000000 'Stop stepper
For j = 1 To toff_seg
pause 5 ' Provisorio
Next j
Endif
Endif
Goto loop2

End
motor_run1:
PORTB = %00110000
'mr1 -> loop motor run1
mr1:
'While PORTB <> %1001000
'WaitMs 250
pause 1 ' Sentido de rotação escolhido pelo 5º switch

'Calcula os passos dados pelo motor
If n_passos <> max_passos Then
n_passos = n_passos + 1
Else
n_passos = 0
Endif

If PORTB = %10010000 Then
PORTB = %00110000
Else
PORTB=PORTB << 1

'Se houver carry põe o bit menos significativo a 1 (RB4)
If PORTB = %10000000 Then PORTB = %10010000

Endif

If PORTB <> %10010000 Then Goto mr1
pause 1
'Wend
Return
motor_run2:

PORTB = %10010000
mr2:
pause 1

'Calculates number of steps
If n_passos <> max_passos Then
n_passos = n_passos + 1
Else
n_passos = 0
Endif

If PORTB = %10010000 Then
PORTB = %11000000
Else
If PORTB = %00110000 Then
PORTB = %10010000

Else
PORTB =PORTB>>1
Endif
Endif
If PORTB <> %00110000 Then Goto mr2
pause 1
Return

'1 minute delay
delay_1min:

i var Byte

For i = 1 To 60
pause 1000
Next i
Return

 

[netbug]

Hi,

I tested the code and the circuit under proteus, and it works fine. I discovered that if I touch the ground with my finger the circuit works fine, if I don't, it works poorly.

So how can I solve a ground problem like this one ?? I am powering the circuit with those transformers that we use to charge a laptop or mobile phone. In this case I am using the power supply from my laptop. How can I make a stable ground from here ?

Please try to answer fast because I want to finish this asap.

Many thanks,

Pedro Cardoso

 

[Nigel Goodwin]

Hi,

I tested the code and the circuit under proteus, and it works fine. I discovered that if I touch the ground with my finger the circuit works fine, if I don't, it works poorly.

So how can I solve a ground problem like this one ?? I am powering the circuit with those transformers that we use to charge a laptop or mobile phone. In this case I am using the power supply from my laptop. How can I make a stable ground from here ?

Please try to answer fast because I want to finish this asap.

Post your complete circuit diagram, don't leave anything out, and we can make suggestions - there's no requirement for a ground connection, so it sounds like you're perhaps picking up hum and interference?.

 

[netbug]

Hi,

I found that I left unconnect two input pins of the pic (because I had no more switchs), so sometimes pic assumed that on of these pics were high. I think I should have grounded these unused pins.

Is there a way to do a small circuit that, if you connect external power, it will use this power; if you disconnect the external power the system will run on batteries without turnning off. Just like mobile phones or laptops do.

Best regards,

Pedro Cardoso

 

[Nigel Goodwin]

Hi,

I found that I left unconnect two input pins of the pic (because I had no more switchs), so sometimes pic assumed that on of these pics were high. I think I should have grounded these unused pins.

What's best to do with unused pins is quite controversial, but the concerns are to do with keeping the lowest supply current. If you don't test the pins in your program, then being high or low makes no possible difference!.

An obvious easy solution, is to make sure you DON'T check unused pins (and why would you?), and if you set the pins as outputs there's no possible problem anyway.

Is there a way to do a small circuit that, if you connect external power, it will use this power; if you disconnect the external power the system will run on batteries without turnning off. Just like mobile phones or laptops do.

A simple diode OR gate is all that's needed, and make sure that the incoming supply is higher than the battery voltage.

 

[netbug]

A simple diode OR gate is all that's needed, and make sure that the incoming supply is higher than the battery voltage.

Hi,

I am not following your idea. Can you be more specific,please. I want to connect the power supply(lets say 12V) or use internal 9V battery. I think the decision must be taken before the regulator. How can I do this with only an OR gate ?

I found a solution for this problem but requires an IC (MAX6326).

**broken link removed**

I also thought of using a relay to switch between the two power sources.

Best regards,

Pedro Cardoso

 

[Nigel Goodwin]

A simple diode OR gate is all that's needed, and make sure that the incoming supply is higher than the battery voltage.

Hi,

I am not following your idea. Can you be more specific,please. I want to connect the power supply(lets say 12V) or use internal 9V battery. I think the decision must be taken before the regulator. How can I do this with only an OR gate ?

I found a solution for this problem but requires an IC (MAX6326).

**broken link removed**

I also thought of using a relay to switch between the two power sources.

As I said, it's VERY simple to do, this is all you need! - your 12V (from a mains adaptor) connects to where it says 'mains in', and the 9V battery connects where it says 'battery in' (or the other way round, it obviously makes no difference). The output feeds to the input of the voltage regulator.

 

[netbug]

Hi,

I am using an ULN2803 to drive a stepper. I want to supply 5v to my stepper, but the output pins of 2803 reach 3V (max). I am connecting the pic to pins 1,2,3,4 of the ULN2803. Pins 9 and 10 of 2803 are connected to gnd and +5V. If I increase the pin 10 voltage to 12V, will I get 5 V at the output of the 2803 ?

Best regards,

Pedro Cardoso

 

[eblc1388]

If I increase the pin 10 voltage to 12V, will I get 5 V at the output of the 2803 ?

NO. The ULN2803 does not give you any output voltage. It is just a open collector transistor with driving transistor (darlington connection).

The function of ULN2803 is like a switch. Its output pin passes current to ground or open circuit, depending on the input.

If you increase the pin10 voltage to +12V, then the ULN2803 can drive a load with +11V or more. So if you want to drive a stepper with 5V, then provide 5-6V for pin 10 and the common coil terminal of the stepper motor.

 

[netbug]

Hi,

Thanks for your answer. But the question is the stepper is rotanting very low speed(1 step every 250 ms), and even this way the torque is very low. As I measured the voltage between common (pin 10) and every output of the 2803, I thought that this low torque would be due to low voltage between common and output pin.

Another question, my stepper is a 5V (I can't remeber the reference) motor from Astrosyn. The point is the 7805 gets very very hot, so I suppose the stepper is sinking to much current. Can I solve this problem using several 7805 in paralell ?

Best Regards,

Pedro Cardoso

 

[eblc1388]

Not knowing which stepper motor you are using , it is difficult to advise you on the power supply issues.

Click the following link to get the Astrosyn stepper motor datasheet and tell us which model you are using in your circuit.

**broken link removed**

 

[Mike - K8LH]

Pedro (Netbug),

I experimented with some 5v/1a stepper motors earlier this year... When I first ran them from a 7805 regulator, my regulator also got very hot and the steppers did not have very good torque... Also, when I tried to drive two coil windings at the same time, the 7805 would shut down...

I suspect multiple 7805 regulators would work ok if your power supply can supply the extra power...

I installed 5 watt current limiting resistors in series with both "common" coil windings and connected these "common" windings to the 12 volt (3 amp) source on the "input side" of my 7805 regulator and the steppers have excellent torque and speed now...

Good luck with your project... Regards, Mike

 

[motion]

Hi,

Thanks for your answer. But the question is the stepper is rotanting very low speed(1 step every 250 ms), and even this way the torque is very low. As I measured the voltage between common (pin 10) and every output of the 2803, I thought that this low torque would be due to low voltage between common and output pin.

Another question, my stepper is a 5V (I can't remeber the reference) motor from Astrosyn. The point is the 7805 gets very very hot, so I suppose the stepper is sinking to much current. Can I solve this problem using several 7805 in parallel ?

Best Regards,

Pedro Cardoso

Before answering this question. Let's sort this stepper motor problem first. Earlier, you said that you're getting about 3V at the output of the 2803. If this is the voltage of the pin w.r.t. ground and your power supply is 5V then the voltage being applied to the motor coils is only about 2V. This should explain why you are getting very low torque.
My advice is to look and study carefully the rating (voltage & current) of the motor. Motors of this type have these values or volts/ohms rating on the sticker at the end cap. From them you can calculate the current requirements. Remember that the ULN2803 is only rated 500mA. I suspect the motor is rated higher than this given the low voltage rating.

I would suggest to look for a higher voltage rated motor (about 12V or higher). This way, the current requirements will be lower for the same torque.

 

[netbug]

eblc1388,

I Can't really remember the reference, but I can assure you that I chose a 5V stepper with 1A max current(I can't remeber the exact value). The problem is I can't download the pdf from astrosyn, there is some error when I try to do it. The stepper I own is an hybrid stepper and can be found in L-series catalog.


Mike, K8LH,

Thank you for your idea. What was the value of the two resistors that you used ? 2.2 ohm ?

Thanks,

Pedro

 

[Mike - K8LH]

Pedro,

If your steppers are 1 amp, are you then driving each coil winding with two '2803 outputs?

I almost used a '2803 for my steppers but I was worried about running two outputs simultaneously at the full 500-ma spec'... I guess I figured that tiny little DIP-18 chip would have to get real hot... I ended up using TIP-122 Darlington transistors and they don't even get warm...

I used 5-ohm 5-watt resistors but they probably should be more like 7 or 8 ohms... Another advantage of the "current limiting" scheme is that when you first energize a coil, it gets a boosted voltage until the current ramps up enough to develop the voltage drop across the resistor... This provides excellent torque...

Regards, Mike

 

[eblc1388]

The problem is I can't download the pdf from astrosyn, there is some error when I try to do it. The stepper I own is an hybrid stepper and can be found in L-series catalog.

I know. The darn website use a broken link. Try replacing the "co.uk" part of the link with "com" and it will work.

Mike, K8LH:

The losses in the transistors will be lower if the current limiting resistors is inserted between Ax & BX & 12V.

 

[Mike - K8LH]

The losses in the transistors will be lower if the current limiting resistors is inserted between Ax & BX & 12V.

Thank you Sir... Regards, Mike

 

[netbug]

eblc1388,

You're right the link is broken because astrosyn.co.uk is down.

Mike, K8LH,

When I bought the stepper I had the specs of the 2803 on my hand, so the stepper must be 500 mA (max). I am sorry for the confusion. But I measured the total current in circuit and it gave me something around 350 mA. The 2803 didn't even get warm, it is cold all the time. The heat problem is only with the 7805.

I will try to put the resistors and I will post again with the correct data from the stepper.

Pedro

 

[eblc1388]

When I bought the stepper I had the specs of the 2803 on my hand, so the stepper must be 500 mA (max).

You would lost around 1.5V across the 2803 at this current. Mike's advice of using two output pins to drive one coil is very good.

Is 7805 on a heatsink and what is the input voltage to 7805? Have you added bypass capacitors on output pin of 7805 to prevent it from oscillating?