AN3288

Firmware design

Doc ID 18011 Rev 2

13/27

3.3

Thresholds system

The software method realized to control the light actuation and prevent accidental switching

due to harsh road conditions is a thresholds system. The implemented strategy is based on

a system of ranges that identifies four main operation zones based on the deceleration

value. Thanks to the filtering procedure explained in the previous paragraph, the brake lamp

does not flicker noticeably when transitioning between two subsequent braking-level

indications.

For the test vehicle used, the four main operation zones have been identified according to

the following patterns:

●

No braking

●

For soft braking: if the deceleration value from an activation threshold is up to 50 % of

the maximum registered value

●

For medium braking: if the deceleration value is included from 50 % up to 70 % of the

maximum registered value

●

For strong braking: if the deceleration value is higher than 70 % of the maximum

registered value

Figure 10 shows how this thresholds range works for the state changing.

Figure 10.

Thresholds system diagram

An activation threshold avoids producing a change in the light actuator, if there is a small

change of the deceleration due to external causes; it can be considered as an additional

filter that further preserves the system from the noise introduced by mechanical vibration

due to harsh road conditions.

The thresholds system C algorithm is:

if(acc<thr3)

/* it corresponds to the maximum braking effort */

{

...

TIM1_SetCompare1(PWM3); /* set the PWM duty cycle to 25% */

brk_stat = TRUE;

...

}