user77467: I'm an Arduino beginner. I've got 2 x 12V DC water pumps
https://www.ebay.co.uk/itm/224461221015
plus 12V, 2A AC/DC adapter to feed them.
I would like to regulate the speed (flow) of the pumps programmatically by Arduino. My first idea was to use 2 channel Relay, however, it only supports two states - on/off. Then I discovered this DC Stepper Motor Driver:
https://www.ebay.co.uk/itm/274521887403
That seems to be a good fit in terms of specifications, but I'm not sure whether it will work with the pumps? It makes me think of whether the DC Stepper Motor Driver may work with only specific motors?
Thanks for any advice!

user68589: Yes, it will work.
You can control the speed of the water pumps with a PWM signal by using:
analogWrite(PWM_pin, value)

Or you can use a cheap transistor like a P2N2222A; here is a full tutorial.

user77467: Unfortunately after trying it does not work as expected. It has been mentioned that it must be a BRUSHED motor and most of these pumps on eBay are Brushless.

77467: <p>I'm an Arduino beginner. I've got 2 x 12V DC water pumps</p>
<p><a href="https://www.ebay.co.uk/itm/224461221015" rel="nofollow noreferrer">https://www.ebay.co.uk/itm/224461221015</a></p>
<p>plus 12V, 2A AC/DC adapter to feed them.</p>
<p>I would like to regulate the speed (flow) of the pumps programmatically by Arduino. My first idea was to use 2 channel Relay, however, it only supports two states - on/off. Then I discovered this DC Stepper Motor Driver:</p>
<p><a href="https://www.ebay.co.uk/itm/274521887403" rel="nofollow noreferrer">https://www.ebay.co.uk/itm/274521887403</a></p>
<p>That seems to be a good fit in terms of specifications, but I'm not sure whether it will work with the pumps? It makes me think of whether the DC Stepper Motor Driver may work with only specific motors?</p>
<p>Thanks for any advice!</p>
 68589: <p>Yes, it will work.</p>
<p>You can control the speed of the water pumps with a PWM signal by using:</p>
<pre><code>analogWrite(PWM_pin, value)
</code></pre>
<p>Or you can use a cheap transistor like a P2N2222A; here is a <a href="https://www.instructables.com/How-to-drive-a-DC-Motor-with-Transistor-Arduino-Tu/" rel="nofollow noreferrer">full tutorial</a>.</p>
 77467: <p>Unfortunately after trying it does not work as expected. It has been mentioned that it must be a <strong>BRUSHED</strong> motor and most of these pumps on eBay are <strong>Brushless</strong>.</p>
