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  1. KrisBlueNZ

    Relay voltage spikes

    Yes, connect the diode as in the diagram in post #20. The diode's current rating needs to be at least as high as the maximum relay coil voltage. Typically people use 1N400x diodes, though the 1N914 / 1N4148 is suitable for small relays. Edit: I meant the diode's current rating needs to be at...
  2. KrisBlueNZ

    6 CELL LI-ION 22.2V BATTERY LEVEL MONITOR

    OK, your calculations are fine except that you need to choose a preferred value that's LOWER than the calculated value, because that will give you a higher current. All the approximations need to be in the direction of increasing the current, because you are trying to meet a minimum current...
  3. KrisBlueNZ

    Driving Peltier Device through L298N to control Temperature

    I think I will stand by my recommendations from post #2 in this thread. That is a power supply that delivers a constant regulated current to the Peltier devices. If you don't want to modify a PC power supply, you may need to build your own switching power supply - either line-powered, or...
  4. KrisBlueNZ

    Driving opamp output to near ground?

    Ah, thank you Laplace. That explains it. So there's no error in the data sheet. I think it's fair to assume that if your load resistance is returned to the op-amp's negative supply rail, the output will be able to get closer to that rail than the specifications show. eem2am, many...
  5. KrisBlueNZ

    Controlling shift register via USB

    I think you should be able to use the parallel FT device. You just need to send bytes to it in the right order, to make sure that the signal you use for shift register data is in the desired state before you assert the signal that's used for shift register clock.
  6. KrisBlueNZ

    Driving opamp output to near ground?

    I think it's a miscommunication in the data sheet. In the first two lines of the "Output" section, the author of the data sheet has combined VOL and VOH onto the same line, and the second line, with the lower RL resistance, has the greater dropout voltage for both VOL and VOH. That is, 45 and...
  7. KrisBlueNZ

    Relay voltage spikes

    cvicente, do you have a reverse-connected diode across the relay coil? If it's a DC relay coil, you should have a diode across it, to clamp the high-voltage spike caused by back EMF from the coil when the relay is de-energised, unless you need the relay contacts to open very quickly, in which...
  8. KrisBlueNZ

    Hard Drive PCB repair

    Have you checked the fuses? There's one on the left, at a 45 degree angle, and another near the top. When the TVS goes short, high current flows and this will blow the fuse. At least it's a possibility. The components you've highlighted in green are "zero ohm resistors" aka links. They should...
  9. KrisBlueNZ

    6 CELL LI-ION 22.2V BATTERY LEVEL MONITOR

    You've calculated a good value for R1 but I don't think you understand the calculations, so I'll explain them in detail. R1 determines the current that flows through the LM336Z. The LM336Z needs at least 0.4 mA in order to regulate properly. The current can be higher than 0.4 mA, but it must...
  10. KrisBlueNZ

    How to vary the power delivered by a pwm signal

    The best source of low-voltage DC at high current is a mains-powered switching supply. There are tons of them available through eBay, though I can't vouch for the quality of any of them! It needs to provide at least a few volts more than the maximum voltage you want to apply to your...
  11. KrisBlueNZ

    How to vary the power delivered by a pwm signal

    OK, you need a variable buck regulator feeding a high-current switch. You can't really control the buck regulator by generating the control signal for its chopper transistor or MOSFET directly with the MCU. The regulator's control IC needs to do this. You CAN control its output voltage using a...
  12. KrisBlueNZ

    Driving Peltier Device through L298N to control Temperature

    Peltier devices are current-driven, and running them at 80% of their rated VOLTAGE will not necessarily cause 80% of the rated CURRENT to flow, because of something called the Seebeck effect, that I know nothing about. The heating or cooling effect is specified based on the current flow, not the...
  13. KrisBlueNZ

    How to vary the power delivered by a pwm signal

    You haven't explained your requirements very clearly. You want to send pulses to a "piece of equipment". A pulse is a signal, but you seem to be implying that these pulses need to have significant power, and you want to use a regulator for them. Do you mean that you want to turn the regulator...
  14. KrisBlueNZ

    PFET gates remain charged

    A few more comments in addition to what Steve has just explained. The normally closed circuit is the problem. MOSFETs, whether P-channel or N-channel, require a gate-source voltage to be applied to them to make them conduct. The difference between them is just the polarity of that voltage...
  15. KrisBlueNZ

    Driving Peltier Device through L298N to control Temperature

    Yes, once the LED is converted into a voltage-controlled component using a current limiting resistor or a linear constant current driver, neither of which is practical at 9A! A high-power current-regulating power supply is required simply to drive a Peltier device. That power supply's output...
  16. KrisBlueNZ

    Driving Peltier Device through L298N to control Temperature

    You can turn the current source ON and OFF using PWM but you can't use PWM in the usual way; for example if the Peltier devices need 15V DC (there are four of them connected in series, and each requires 3.75V DC), you can't use a 20V DC supply and PWM it at 75% to get an equivalent heating or...
  17. KrisBlueNZ

    connection of a thermal sensor TC1047AVNBTR to the microcontroller MSP430F4618

    I don't understand your question. The temperature sensor does not have to be connected to AVREF. You want to connect the output from your temperature sensor to an input of the ADC in the MSP430FG4618, right? So you need to connect the temperature output to a MSP430FG4618 pin that can be...
  18. KrisBlueNZ

    Driving Peltier Device through L298N to control Temperature

    There are several reasons why your idea won't work. Mainly, because you can't drive Peltier devices using a pulse-width-modulated signal because they are not ohmic in any sense; their voltage vs. current graph is nothing like a resistor. I haven't investigated whether you can parallel L298N...
  19. KrisBlueNZ

    Designing a regulator?

    Another option would be to buy a modern wall wart that uses a regulated switching supply circuit. These are relatively cheap, fairly accurate, and light and compact.
  20. KrisBlueNZ

    connection of a thermal sensor TC1047AVNBTR to the microcontroller MSP430F4618

    Are you saying that can only use the RF1 and RF2 connectors? None of the pins on those connectors are connected to pins on the MSP430FG4618 that can be connected to ADC inputs, so you will not be able to connect your temperature sensor through those connectors. Look at the MSP430FG4618 data...
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