ULN2803a best practice

Started by "David E. Basile" October 3, 2006
I'm getting back into the BasicX and old age keeps me from retaining a lot
of information .

I have a a ULN2803a and I'm trying to fire some 24vdc air valves so I have a
few questions. I'm not sure what the current rating on the valves are

1) I have several 12vdc relays and I'm wondering if it would be better to
drive the relay to trip the valve or just use the 2803 to drive the valve?
2) Do I need any type of resistor on the input side of the 2803? (I've seen
them use a 4.7k resistor when using the 2803 with a parallel port)
3) Do I need any type of zener diode across the valve coil to prevent
spiking?
4) Do I need any type of capacitor between pins 9 and 10 (Again I've seen
them use a .01uF on another project)

Sorry if these are easy questions but I just want to make sure I don't
destroy the BX24.

Thanks in advance.
David
Sort of. If your 24v valves draw the same current (380mA) as mine do then
you can't drive them with a single output of the 2803. However the docs say
you can gang outputs together, so just tie two outputs together for each
solenoid.

1) nah, skip the relays.

2) I did not use a resistor on the input. The data sheet doesn't seem
to call for one (at least the 2003 datasheet)

3) I don't think so - I think the 2003 takes care of it. Just make
sure you tie Pin9 of the 2803 to your +24 rail.

4) I don't know on this one. Perhaps someone more EEish can chime in?

I used an opto-isolator and I recommend you do the same, to physically
separate the very expensive BasicX from the high-voltage stuff as well as to
eliminate any line noise that the solenoids are likely to introduce.

Good luck!

DougM

_____

From: b... [mailto:b...] On Behalf Of
David E. Basile
Sent: Monday, October 02, 2006 5:38 PM
To: b...
Subject: [BasicX] ULN2803a best practice

I'm getting back into the BasicX and old age keeps me from retaining a lot
of information .

I have a a ULN2803a and I'm trying to fire some 24vdc air valves so I have a
few questions. I'm not sure what the current rating on the valves are

1) I have several 12vdc relays and I'm wondering if it would be better to
drive the relay to trip the valve or just use the 2803 to drive the valve?
2) Do I need any type of resistor on the input side of the 2803? (I've seen
them use a 4.7k resistor when using the 2803 with a parallel port)
3) Do I need any type of zener diode across the valve coil to prevent
spiking?
4) Do I need any type of capacitor between pins 9 and 10 (Again I've seen
them use a .01uF on another project)

Sorry if these are easy questions but I just want to make sure I don't
destroy the BX24.
Thanks in advance.
David
Hi,

For your information and consideration.

I am using the BasicX in my projects and right now I am driven six solenoids 24 volts - 2 amps using 6 TIP121 darlington transistors with a 1k resistor connected from the basicx pin to the base of the darlington transistor with no problem.

The TIP121 is a darlington transistor with a collector to emitter diode protection. You must put a diode across the solenoid to avoided negative spikes when de-energizing the solenoids. if not will burn the transistor. The TIP 121 can handle 60 volts 5 amps.

I like to minimizes the circuit parts to a minimum, that's why I used the transistor alone with an interface resistor between the Basicx pin and the transistors to protect the basicx pin output.
.
Attached is a drawing in word. Sorry but the drawing is the best that I can do.

Hoping this will help you.

rosarite

-----Original Message-----
From: d...@comcast.net
To: b...
Sent: Mon, 2 Oct 2006 9:05 PM
Subject: RE: [BasicX] ULN2803a best practice

Sort of. If your 24v valves draw the same current (380mA) as mine do then
you can't drive them with a single output of the 2803. However the docs say
you can gang outputs together, so just tie two outputs together for each
solenoid.

1) nah, skip the relays.

2) I did not use a resistor on the input. The data sheet doesn't seem
to call for one (at least the 2003 datasheet)

3) I don't think so - I think the 2003 takes care of it. Just make
sure you tie Pin9 of the 2803 to your +24 rail.

4) I don't know on this one. Perhaps someone more EEish can chime in?

I used an opto-isolator and I recommend you do the same, to physically
separate the very expensive BasicX from the high-voltage stuff as well as to
eliminate any line noise that the solenoids are likely to introduce.

Good luck!

DougM

_____

From: b... [mailto:b...] On Behalf Of
David E. Basile
Sent: Monday, October 02, 2006 5:38 PM
To: b...
Subject: [BasicX] ULN2803a best practice

I'm getting back into the BasicX and old age keeps me from retaining a lot
of information .

I have a a ULN2803a and I'm trying to fire some 24vdc air valves so I have a
few questions. I'm not sure what the current rating on the valves are

1) I have several 12vdc relays and I'm wondering if it would be better to
drive the relay to trip the valve or just use the 2803 to drive the valve?
2) Do I need any type of resistor on the input side of the 2803? (I've seen
them use a 4.7k resistor when using the 2803 with a parallel port)
3) Do I need any type of zener diode across the valve coil to prevent
spiking?
4) Do I need any type of capacitor between pins 9 and 10 (Again I've seen
them use a .01uF on another project)

Sorry if these are easy questions but I just want to make sure I don't
destroy the BX24.

Thanks in advance.
David





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ULN2803 current sink per pin is 500mA (600mA peak) at
up to 30v (50v max).
4k7 base resistors are built in, so you can connect it
direct to a BX.
Also anti-spiking diodes are built in and commoned on
pin9 which needs to go to V+ of the coils.
All the pneumatic valves on the Shadow biped were
driven by ULN2803s at 50v (max V!!!), directly
connected to the electronics, no optos, and we never
had any problems.
Google for the data sheet pdf for connection examples.
David

__________________________________________________
I really meant the diodes were commoned on pin10 which
should go to motor V+, pin9 is of course GROUND !!! Sorry.

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