Testing a ULN2003A before connecting to a PICAXE

[Celestialsphere]

Hello everyone,

As a newbie I am trying various different circuits on a breadboard before hooking the completed circuit up to a PICAXE.

I have assembled a ULN2003 with an resistor/LED on an output. The circuit is on 4.5VDC. My question is how can I switch the input without using a PICAXE - ie what's required between the positive rail and the input to switch the transistor on and therefore the LED?

I have searched high an low for a test circuit but all I could find was those with inputs toggled high by a PIC output of some kind.

I hope a friendly PICAXEr can help me.

Sorry if it's a silly question.

Cheers

Andrew

 

[westaust55]

Welcome to the PIACXE forum.

If you wish to test a channel manually, then connect a resistor (eg 10 kOhnm) from the input to ground so the pin is not floating.
Then use a switch from +5V to the input. When the switch is closed, the Darlington transistor for the selected channel will turn on. Note that the ULN2003 already has a 2.7 kOhm resistor between the input pin and the transistor base.

Be aware that the output only pulls the output to ground (0 volts) when active so your LED and series resistor must be connected between +5V and the ULN2003 output.

The ULN2003 datasheet can be found here:
http://www.datasheetcatalog.org/datasheet2/f/0c6x6a46ig46qlxf3j2qsaii8o3y.pdf

It will always be good to track down the datasheet to understand how a part works. If it is not a regularly used chip, then it helps to give a link to the datasheet yourself as by saving others having to search for a datasheet means they have more time to help you and many folks can be pressed for time here.

There is no such thing as a 'silly' question – particularly for newcomers to electronics.
All PICAXE forum members here are friendly (maybe some more than others - shades of Animal Farm ). Occasional some may get a bit “strained” when the same question arises too often in a row, but you will never to told to go elsewhere when asking PICAXE and related circuit questions.

 

[fernando_g]

I congratulate you on taking the time to check your circuit's sections individually before hooking everything up. That is an intelligent approach. It is a little more time consuming, but prevents the magic smoke from coming out of the components.

 

[Celestialsphere]

Success !

Thankyou for the encouragement and information guys.

Using westaust55's info I successfully tested the circuit. This is a diagram of circuit driving an LED for the benefit of others.



Cheers

Andrew

 

[westaust55]

Great to read you test has worked.
In response to your separate PM, the circuit in your schematic is totally acceptable for test purposes.