# Tag Info

20

This device is far more than "just a resistor ladder". It includes a great deal of digital logic that controls the serial interface and allows you to program the resistance. The resistors are connected to the "wiper" by analog switches. These switches are made of transistors. There are parasitic PN junctions between the transistor terminals and the power and ...

7

This is a real proper way of doing it for the pedants amongst us (and that usually includes me). Use two comparators (one for the high level threshold and one for the low level threshold). Use two DACs (or digipots) to set the thresholds for each comparator. Feed the input signal into both comparators. The two comparator outputs can be used to set a flip ...

6

A series combination of power-of-two resistors will accomplish what you want, though with n resistor values of n resistors for n bits. So 20 resistor values will give you from 1 ohm to 1.048575 Megohm in steps of 1 ohm (however it will surely not be monotonic!). The n'th resistor from 0 to 19 would be $2^n\Omega$, so 1$\Omega$, 2$\Omega$, 4$\Omega$,...

6

The 5ppm is only a typical spec, and there is no guaranteed maximum. Also the 35ppm is a typical spec (of total resistance drift). Note that the 3-sigma element resistance drift over lifetime is in the hundreds of ppm so some parts can be pretty bad. You don't see those changes directly in your configuration but they can result in side effects if there are ...

5

It looks like you have the SHDN pin tied to ground. The bar over the SHDN label means it is active low. This means that tying it to ground activates that circuit. According to page 20 of the data sheet you linked above, that will open circuit the devices. "Both parts have a power shutdown SHDN pin that places the VR in a zero-power-consumption state where ...

5

Ignoring the details of working through the 'unique' interface of LabVIEW, I would suggest using a simple binary search algorithm. Set the pot to mid-scale, determine whether the null point lies in the lower or upper half of scale, then set the new upper and lower bounds, and repeat. Assuming your measurements are stable (you will have to program a ...

4

You will likely not find such a part because there will always be some kind of electrical switch in a digital potentiometer, and these always have some built-in resistance. You can however compensate the resistance. You've already linked one article that shows it, but you can improve upon that. A single OpAmp and three resistors can work as a negative ...

4

For each 16 bit device (other than the final one) put a single D type flip flop on the output and use it's output as feed to the next 16 bit device. The d type will soak up each 17th bit or, looking in a different way, the d type makes the 16 bit device a 17 bit device.

4

Digital potentiometers are (in their output stage) linear devices used to set a voltage division / resistance ratio through a switched set of resistive elements. They are generally low current, normally very linear, relatively low noise (although not as low as a high specification real potentiometer) and useful for signal-level processing. PWM with a (...

4

Circuit modified. sources commoned and R& D added. May well work without R3 - see below. R3 value not shown but could be 10M or higher if environment allows. R2 can be lower if desired. Needs thinking but workable (I believe). It's the sort of circuit that can be made to work entirely reliably but which 'has things to think about along the way'. The ...

4

Here's one potential reason: You're sending an audio signal with a +12 V DC offset into an IC that is designed for much lower voltages. EDIT: Here is brhans' solution: simulate this circuit – Schematic created using CircuitLab

4

I think you're good to go. A few points I noticed tho'... your SDO requires a pullup. So clock speed needs adjustment accordingly (see datasheet) the 'mega SDO will be driving 8x chips, but I think it should be ok. use standard best practices in terms of PS decoupling and layout. datasheet mentions SPI 'compatible'. I could not quickly find where the ...

4

A couple of SPST relays will do what you want: simulate this circuit – Schematic created using CircuitLab By default (no relays activated), the 100k protection resistor is in the circuit. Activate RLY1 to make a measurement. Activate RLY2 to operate.

4

If your microcontroller does not have a DAC, you can generate high-frequency pwm, run it through a low pass filter and it is effectively an analog voltage. Unfortunately if you're trying to get up to a higher rail voltage than your microcontroller pin output, then you could either first pwm a transistor in front of the filter with a pull down from a higher ...

3

Do you have a need for a particular value? Normally it is better to use a Digipot in potentiometer mode (using all three pins) than in rheostat mode (just two pins as a variable resistor). The potentiometer mode will be more accurate and suffer less from variations with temperature. When using potentiometer mode in most circuits the actual value is ...

3

The MCP4017 is a 7 bit digital pot. That means it has 127 steps between the low end and the high end of the pot resistance. The 5k, 10k, 50k and 100k options refers to the total resistance between the low and high ends. So if you get the 100k pot, it provides 100,000Ω / 127 Steps = ~787Ω per step (linear pots). This is how all digital pots work, accounting ...

3

No, you can't do that without using a separate isolation circuit between the logic circuit and the digital pot. I've never seen a digital pot that also had that type of isolation built in.

3

Since the - input of the opamp will be at GND, (zero volts) no matter what, the opamp's output voltage will change in order to force enough current through the AD5241 to keep the - input at zero volts, no matter what the diode's doing. So, if the AD5241 is sitting at, say, 1 megohm and everything is stable, then if you shunt the AD5241 with 1 megohm, the ...

3

What would you be trying to improve? Performance? Cost? Availability? There are no guarantees on the noise, the offset drift with temperature, the gain tempco. There is a guarantee on the gain error. The typical noise is not bad for a CMOS-input type. The typical gain tempco is excellent (4ppm/K), but no indication of the drift with time. Offset ...

3

Be aware of the capacitance to ground on each pin of the digital pot. The spec you embedded in your question suggest a range in the order of about 100pF. I don't know the exact switching frequency of your proposed application but, if it were 200kHz, 100pF would have an impedance of about 8 kohms (reactive) and this might be significant compared to the ...

3

Completely replacing R1-R2 with a DAC may give you mixed results because the circuit saves a part by relying on the voltage divider's parallel impedance R1||R2. You'll need to ensure that the DAC has the same output impedance as seen from R3. simulate this circuit – Schematic created using CircuitLab That will adjust the threshold while keeping the ...

3

You can replace the jumper with an analog switch, however it will add some temperature sensitivity and voltage sensitivity of gain (nonlinearity or distortion depending on how you think of it). However since you're using LM358s you are not too concerned about either of those, so run the numbers and see if it works for you. There are -thousands- to choose ...

3

How can I make a digital audio panning controlled by a microcontroller? Try using this circuit: - But scale up the resistors to suit your pot. The down side of using a digital pot is the wiper resistance. For the MCP4141 (100K) you used, it has a wiper resistance of up to 300 ohms, so there will be a small amount of leak through on the "muted" channel. I ...

3

As @alex.forencich suggested, I have also tried setting CS to LOW for the whole duration of the data transferring process (for all 16 bits) and removed the odd MOSI <-> MISO switching, ending up with the code like this... int SPITransmitData(unsigned char data) { PORTB &= ~((1 << SCK) | (1 << MOSI)); int received = 0; for ...

3

Second option is a good representation. You can fabricate well matched resistors in CMOS processes, and also well matched analog switches. As ever, the absolute value tolerance for passives in CMOS is high, but the matching is excellent. Have a look at the datasheet for the PGA2311, which is a audio potentiometer. The first option would be a bit grim, as ...

3

Maximum voltage on the digital pot resistive elements is +5V, as specified in the X9C103 datasheet. There are other digital pots which can deal with higher voltages, but also keep in mind the minimum load current on the LM317, which may be too much for a digital pot if you try to use the resistive divider for that purpose. Edit: One way to do something ...

2

You should be fine with a DPOT in the voltage divider. However, do not replace the entire divider with a DPOT. The voltage on the DPOT pins cannot exceed the power rails. I would suggest replacing only the lower half of the voltage divider with the DPOT; this will ensure that the maximum voltage the DPOT can see is the reference voltage of 1.2 volts. In ...

2

You need to implement a custom usb Peripheral. You can use standard USB CDC (the usb to serial protocol) and have a microcontroller interpret commands sent through a virtual com port to control the digital pots and push back results.

2

Looking at the MC-60 schematics online, it looks like the potentiometer just generates a DC voltage. But the most important thing is that the potentiometer is not isolated from the mains power. Edit: Here is the schematic (right click, "view image" to see a readable version). Notice there is no isolation transformer between AC1 and AC2 and the rest of the ...

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