OpenSprinkler › Forums › Hardware Questions › OpenSprinkler › Query with the firmware driving of the DC board › Reply To: Query with the firmware driving of the DC board
I don’t fully understand the problem, but here are a few notes to begin with:
– BPE is the booster power enable pin, when it’s high, the input DC voltage is fed into MC34063 booster to generate boosted voltage.
– BVE is the booster voltage enable pin, when it’s high, the boosted voltage from the 2200uF capacitor is dumped to the COM line, to provide impulse voltage for the solenoids to engage.
– Between the input DC voltage and COM, there is a SS34 diode, this way, as the boosted voltage fades away, the input DC voltage will continue to provide holding current for the solenoids to keep engaged. As long as BPE is turned LOW after the initial impulse voltage, it doesn’t matter if BVE stays HIGH or not, because the voltage from 2200uF will eventually fall below input DC voltage, hence the input DC voltage will take over to provide current to the solenoids. On the other hand if BPE stays high, the booster will continue to try to bump the voltage, and that can be a problem.
– The only thing I can think of, regarding 7805 drawing a lot of current, is that something on the +5V line is drawing a lot of current. But if you look at the schematic, there isn’t that much connected to the +5V line: the booster is connected to the input DC voltage, so that comes directly from the power supply and not drawing from +5V. Also, as long as the input DC voltage is higher than 5V (we use 7.5V by default), the current shouldn’t flow backward from 5V to the input.
– We are aware that if the controller has a wired Ethernet module connected, it can draw a lot of current — because the wired Ethernet module itself draws 180mA, and the WiFi chip further draws 70mA, that’s about 250mA at minimum. For this reason, if wired Ethernet module is connected, we recommend the input DC voltage to be as low as possible: 7.5V is ideal, 9V is probably ok, but 12V would be too high as that will put too much heat dissipation on 7805. Even without wired Ethernet module, the DC voltage should not be higher than 12V, again, to minimize the power dissipation on 7805.
What is your input DC voltage? Even at 300mA current, if the input voltage is only 7.5V, that power dissipation shouldn’t be more than (7.5-5)*0.3 = 0.75W (probably a bit lower than this because there is a diode D1 that drops maybe 0.5V). Do you have anything else connected on the +5V line?