The buffer that holds its ground
Compare a loaded divider with and without a voltage follower.
Difficulty: Breadboard. Estimated build time: about 30 minutes. 7-line bill of materials. Compare supplier offers when available. Use an LM358P voltage follower to reduce loading of a weak signal source.
Prepare the bench
Use an isolated, regulated 5 V source with a 20 mA current limit and a digital voltmeter with approximately 10 MΩ input resistance. These are bench tools, not included in the shopping list. Disconnect power before changing connections. Confirm breadboard rail continuity and check for supply shorts before powering up.
Power and identify the IC
Use the TI LM358P in an 8-pin PDIP, viewed from above with the notch at the top. Pin 8 goes to +5 V and pin 4 to ground. Put 100 nF directly between pins 8 and 4. For the unused amplifier, connect pin 5 to Vin and pin 6 to pin 7; leave pin 7 otherwise unloaded. Do not substitute a different package without checking its drawing.
Make Vin and close feedback
Make Vin with 33 kΩ from +5 V to Vin and 10 kΩ from Vin to ground, giving about 1.16 V. Connect Vin to pin 3. Connect pin 1 directly to pin 2. Pin 1 is the output; measure it relative to ground. Keep every input in this low-voltage range.
Compare source loading
With power off between changes, connect 1 kΩ from pin 1 to ground and measure: the output should remain near 1.16 V. Remove that load, then connect it directly from Vin to ground: the divider alone falls to about 0.134 V. Restore the buffered connection. The follower is not a power amplifier and must not be shorted.