How to Connect an Ammeter on a Bread Board
Bread boards are a popular test bed for electronics experimentation. They allow the experimenter to change parts easily without soldering as he fine tunes the circuit he wishes to optimize. Most bread board kits include a voltmeter or a DMM (Digital MultiMeter). Some include an Ammeter for measuring current as well. This article will show how to connect the ammeter and discuss ways to avoid damaging the meter.
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Things You'll Need
- Bread board kit
- Circuit being tested
- Test leads for the ammeter
- Sensing resistors (1 ohm precision resistor, 0.1 ohm 10 Watt power resistor)
- Voltmeter or DMM (Digital MultiMeter)
Instructions
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How to connect an Ammeter on a Bread Board
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1
Mount the ammeter onto or near the bread board (if it is not already part of the bread board kit), using the ammeter's bezel (mounting frame) and wood or metal screws as appropriate for your bread board kit.
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2
To read current in the part of the circuit you wish to test, turn off power to the circuit and remove that leg of the component (resistor, diode, transistor) from the bread board post where it is attached.
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3
Compare the range of current you expect to see in that part of the circuit to the maximum current rating for your ammeter. If the expected current exceeds the rating of the ammeter, you may damage the ammeter and should use a sensing resistor instead of making a direct reading. If the expected current is within the ammeter's rating, go to Step 4. If it is not, go to Step 6.
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4
Connect the positive lead of the ammeter to the lifted component lead and the negative lead of the ammeter to the post from which the component was removed. The ammeter is now in series with that part of the circuit. Return power to the circuit and the ammeter will show the value of the current flow. Note: if the ammeter needle tries to swing below 0, remove the power and put the positive ammeter lead on the post and the negative ammeter lead on the component leg (reverse the meter polarity) and return the power for a positive reading.
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5
Record your current reading. Remove the power from the circuit. Remove the ammeter leads and reconnect the lifted component leg to its bread board post. Continue with your tests.
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6
If the expected current will damage the ammeter, use a current sense resistor at the point of interest rather than inserting the ammeter into the circuit.
Insert the sense resistor (1 ohm precision resistor, if power at the measuring point ( voltage x current) would be less than 0.25 Watts or the 0.1 ohm 10 Watt, if power would be between 0.25 and 10 Watts) between the component lead and the bread board post.
Using the voltmeter (or DMM), measure the voltage drop across the resistor.
If using the 1 ohm resistor, the voltage across the resistor would match the current (25 mV shows a 25mA current). If using the 0.1 ohm resistor scale, the reading times ten (25mV shows a 250mA) is the current flow at the point of measurement.
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