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If you can tolerate the cost of buy vs build then the Dimension Engineering Sabertooth range of motor controllers are popular.If you have a limited number of PWM pins then off-loading the control to another board 'may' be attractive
What's your budget? Pololu has lots of controllers that require two pins; one PWM for speed and one high/low for direction, with a variety of voltage/current options. Buy them, drop them in, done!If you want to build your own, the easiest way to go is to use the lm298 as a gate driver for power MOSFETs. Instead of driving the motor wires, have it drive a complementary pair of power MOSFETS (P-channel and N-channel) on each side. The lm298 and the MOSFET voltages must be the same, so that the driver can get close to the source voltage of the P-channel to turn it off.Also remember that such a drive situation will be the inverse of what the lm298 itself is driving -- high output will mean that the N-channel will conduct and drive the driven load low.Finally, a motor controller with serial inputs will require only a single pin from your microcontroller -- if you don't have a spare UART, then something like SoftwareSerial may be good enough. Various controllers are available that take serial inputs, including ones from Pololu, Dimension (Sabretooth,) and Orion (RoboClaw.)
Microchip has a few App Notes on Motor drivers and H-Bridge control logic.To use less pins from the processor you just need some logic to set each of the four MOSFET's to the correct states with a PWM and a direction input.When I build discrete H-Bridges I include this extra logic to ensure a programming mistake does not put the H-Bridge into a 'smoke' state. It also saves pins and makes coding the motor control simpler.
For basics on motor driving (good back ground reading):AN905, AN898AN807 uses an TC4469 for simplifying the control logic. In fig 1 note the PWM (from the 555) and the direction signal. Then look at the data sheet for the TC4469 for some additional info.There are a few other App Note that deal with feed-back and PID control that are interesting.Those circuits in your links do not help you save processor pins or simplfy the control circuits. They do use MOSFET gate driver chips that are useful to drive larger MOSFETs. Those circuits can be used with the logic in AN807.