CA Zuke wrote:> > Hi, > > Can someone PLEASE tell me what the current (Amperes) should be for > powering a pic? > > I use a L7805 voltage regulator but it still seems like I can get a > whole range of different levels of current depending on the batteries > use. (also you get different Amps for the L7805. Some are 0.1A and > others are 1A or even 2A) > > I have 4 1.2V 1800mA batteries but I guess that current is far too > high. The 9V rechargable I have is 150mAh. How is it possible that the > 9V has so little curent compared to he 1.2V??? I aways thought 9V is > stronger? > > Anyway.. I really want to power my pic off a battery. So please let me > know what the current and voltage should be. > > Thanks in advance > CE AUKEI run a PIC16F628, four EEPROMs, and one LED (LED is ON for only 100ms ever sec.) from a 9v (actually 7+ volt) NiCd battery. LED anode is connected to the 78L05 output through several hundred ohms resistor, LED cathode is connected to a PIC pin which pulls it low to turn the LED on. I have used this circuit for about a year and it works fine. As long as the total current of your circuit never exceeds the current-supplying capability of the battery or the 78L05, your circuit should work fine too. "Just do it." Michael
Pic Currrent
Started by ●October 15, 2004
Reply by ●October 24, 20042004-10-24
Reply by ●October 24, 20042004-10-24
Missed the orginal post - but a PIC should onil draw nano amps in sleep mode and ma as required by the circuit otherwise. The following is a reply to the same problem discussed in another newsgroup. pick a resistor that you believe will drop a tolerable amount of voltage at the average current. For example, if you believe the average current is 150uA, you might pick 1K 1% which will drop 150mV at that current. Then put a capacitor across it to smooth the reading at the repetition rate of whatever pulses etc. are being drawn from the supply. Maybe you pick a time constant of 1 second, so 1000uF electrolytic. This is a single pole LPF. You use the meter in voltage mode, of course. In stubborn cases, you may wish to add a second pole, say a 100K resistor and 10uF tantalum. That won't affect the reading with a >10M input Z, the average current is still 1mV/uA within a couple of percent. If the voltage turns out to be too large or small - so it drops too much voltage to the circuit, or the voltage is too small to measure easily, then just change it (and the capacitors) Note that if current is drawn in short pulses you have to make sure that the instantaneous decrease in the voltage is not too high or the reading may be inaccurate or the circuit may malfunction. A 'scope is useful in this regard. You can also calculate it to bracket the problem. Eg. Supply the 150uA is essentially all composed of pulses: 150mA for 200usec with a 200msec period. A 100uF capacitor would see a voltage change at the terminals of delta-V = I * Ton/C = 300mV, which is a bit high. The 1000uF would yield a more reasonable 30mV, so the troughs would be 180mV down from nominal, not 450mV down. The 30mV/300mV p-p of ripple will yield jumpy readings as the 5Hz frequency "beats" with the measurement cycle of the meter. This is where the second pole filter comes in handy. Roy