I am using PIC18F26K83 which has 12 bit ADC in it and I want to measure voltage values on a specific pin. Voltage values will be between 10 V and 30 V. I supply my MCU with 4.9 V. And from my research it is equivalent to voltage reference ( I am not sure in this point.). Which means if the voltage value on the a pin is 4.9 V I will get 4095 from ADC and if the voltage value is 2.45 V ADC value will be 2048. Is it correct? My main question is: can I measure voltages that are between 10 V and 30 V with 4.9V voltage reference? If no, is there a way to measure that range with ADC without changing the voltage reference? Thanks.
Edit: So I added a voltage divider circuit now I divide that voltage by 11. In that case calculations looks like: (4.9 * adc_out / 4096) *11 = voltage_value.
It looks like only way is to use voltage divider. We can close the topic.
Yes, you need a hardware divider circuit to measure 10V.
And please have a look at the Absolute Maximum Ratings in the Electrical Spezifications:
The maximum voltage for any pin is VDD + 0,3V !!!
So any higher voltage will destroy the chip.
Related
I'm trying to change pin voltage on 'Altera cyclone 4 FPGA' in Quartus? I have changed it in a pin planner and source voltage. But, unfortunately, the voltmeter always show '3 - 3.3 V'.
Am I missing something. Please, advise.
You can't change pin voltages from Quartus. The I/O voltage is equal to the voltage you supply at VCCIO (for that particular I/O bank).
The Quartus setting is to tell the design tools what voltage your hardware will be using so that timing and power consumption calculations will be correct.
As shown by this table in the device datasheet, the I/O Standard and VCCIO voltage level are linked, you cannot select an I/O standard at a different voltage without changing the I/O supply voltage your PCB provides to the FPGA VCCIO pins.
I have a raspberry and an auxiliary PCB with transistors for driving some LED strips.
The strips datasheets says 12V, 13.3W/m, i'll use 3 strips in parallel, 1.8m each, so 13.3*1.8*3 = 71,82W, with 12 V, almost 6A.
I'm using an 8A transistor, E13007-2.
In the project i have 5 channels of different LEDs: RGB and 2 types of white.
R, G, B, W1 and W2 are directly connected in py pins.
LED strips are connected with 12V and in CN3, CN4 for GND (by the transistor).
Transistor schematic.
I know that that's a lot of current passing through the transistors, but, is there a way to reduce the heating? I think it's getting 70-100°C. I already had a problem with one raspberry, and i think it's getting dangerous for the application. I have some large traces in the PCB, that's not the problem.
Some thoughts:
1 - Resistor driving the base of the transistor. Maybe it won't reduce heating, but i think it's advisable for short circuit protection, how can i calculate this?
2 - The PWM has a frequency of 100Hz, is there any difference if i reduce this frequency?
The BJT transistor you're using has current gain hFE of roughly 20. This means that the collector current is roughly 20 times the base current, or the base current needs to be 1/20 of the collector current, i.e. 6A/20=300mA.
Rasperry PI for sure can't supply 300mA current from the IO pins, so you're operating the transistor in linear region, which causes it to dissipate a lot of heat.
Change your transistors to MOSFETs with low enough threshold voltage (like 2.0V to have enough conduction at 3.3V IO voltage) to keep it simple.
Using a N-Channel MOSFET will run much cooler if you get enough gate voltage to force to completely enhance. Since this is not a high volume item why not simply use a MOSFET gate driver chip. Then you can use a low RDS on device. Another device is the siemons BTS660 (S50085B BTS50085B TO-220). it is a high side driver that you will need to drive with an open collector or drain device. It will switch 5A at room temperature with no heat sink.It is rated for much more current and is available in a To220 type package. It is obsolete but available as is the replacement. MOSFETs are voltage controlled while transistors are current controlled.
I use the PIC16F88 for my project, with XC8 compiler.
What I'm trying to achieve is to control 4 LEDs with 4 buttons, when you press a buttons it increases the duty cycle of the corresponding LED by 10%.
When you press the button on RB0 it increases the duty cycle of the LED on RB4, and so on.
Every LED is independent, therefore it can have a different duty cycle.
The problem is that the PIC i'm using only have one PWM module on either RB0 or RB3 (using CCPMX bit).
After some research I decided to implement software PWM to have four different channels, each channels would control one duty cycle, but most of the sources I found didn't provide any explanation on how to do it.
Or is there a way to mirror PWM to multiple pins ?
Thanks by advance for helping me out.
Mirroring is not an option.
PWM is relatively simple. You have to set PWM frequency (which you will not change) and PWM duty cycle (which you need to change in order to have 0-100% voltage range). You have to decide about resolution of PWM, voltage step that you need (built in PWM for example is 8-bit and has 0-255 steps).
Finally, you have to set timer to interrupt based on PWM frequency * PWM resolution. In Timer ISR routine you need to check resolution counts and PWM value of all your channels. Resolution count will have to reset when resolution value is reached (and start to count from 0 again, all outputs go HIGH here, also). When PWM value of output is reached you have to toggle (pull it LOW) corresponding pin (and reset it back to HIGH with every resolution count reset).
This is only one way of doing it, involves only one timer and should be most simple since your PIC is low with resources.
Hope it helps...
I have been using FRDM_KL46Z development board to do some IR communication experiment. Right now, I got two PWM outputs with same setting (50% duty cycle, 38 kHz) had different voltage levels. When both were idle, one was 1.56V, but another was 3.30V. When the outputs were used to power the same IR emitter, the voltages were changed to 1.13V and 2.29V.
And why couldn't I use one PWM output to power two IR emitters at the same time? When I tried to do this, it seemed that the frequency was changed, so two IR receivers could not work.
I am not an expert in freescale, but how are you controlling your pwm? I'm guessing each pwm comes from a separate timer, maybe they are set up differently. Like one is in 16 bit mode (the 3.3V) and the other in 32 (1.56v) in that case even if they have the same limit in the counter ((2^17 - 1) / 2) would be 50% duty cycle of a 16 bit timer. But in a 32 bit, that same value would only be 25% duty so, one output would be ~1/2 the voltage of the other. SO I suggest checking the timer setup.
The reason the voltage changed is because the IR emmiters were loading the circuit. In an ideal situation this wouldn't happen, but if a source is giving too much current the voltage usually drops a bit.
I have a clock of 100 mhz. I want to use DCM to create a clock of 78 mhz.
I think I should use two DCM, where the output of first DCM goes into the second DCM but I don't know if this will work.
Best Regards
Rather than using a DCM directly you can investigate using a Direct Digital Frequency Synthesizer (DDFS). It amounts to an accumulator that is incremented by a constant count value. You can control the precision by the size of the accumulator.
It is helpful if there is as much disparity between the accumulator clock and the generated frequency as possible. Consider using a DCM to scale the 100MHz up to the highest speed you can run a counter of the necessary width and still meet timing for your target device. There will be some jitter equal to one period of whatever clock is driving the accumulator but the average frequency can be made very close to 78 MHz.
accum_freq = 100 MHz * DCM_MULTIPLIER
accum_size = ceil(log2(accum_freq / (78 MHz * tolerance)))
increment = 78 MHz / accum_freq * 2**accum_size
accum = accum + increment
You then tap off the MSB of the accumulator to get your synthesized 78 MHz clock.
You can either manually compute these constants for use as magic numbers or do the arithmetic natively in VHDL to define the size and increment as machine computed constants. By reducing the tolerance you will increase the required size of the accumulator. Start off with 0.01% (0.0001) and see if it is satisfactory.
What device are you targeting? On a Spartan-6 the DCM_CLKGEN allows a multiplier of 39 and a divider of 50, which gets you your 78MHz.
If you set your multiplier to 7 and your divider to 9 you'll be able to get to 77.77 MHz. Will that work for you?